pytest: make hold_timeout.py test plugin release on a prompt, not timeout.

diff --git a/tests/plugins/hold_invoice.py b/tests/plugins/hold_invoice.py
index b3a0f376..15553cab 100755
--- a/tests/plugins/hold_invoice.py
+++ b/tests/plugins/hold_invoice.py
@@ -3,6 +3,7 @@
 """
 
 from pyln.client import Plugin
+import os
 import time
 
 plugin = Plugin()
@@ -10,9 +11,10 @@ plugin = Plugin()
 
 @plugin.hook('invoice_payment')
 def on_payment(payment, plugin, **kwargs):
-    time.sleep(float(plugin.get_option('holdtime')))
+    # Block until file appears
+    while not os.path.exists("unhold"):
+        time.sleep(0.25)
     return {'result': 'continue'}
 
 
-plugin.add_option('holdtime', '10', 'The time to hold invoice for.')
 plugin.run()
diff --git a/tests/test_pay.py b/tests/test_pay.py
index 6b6875f3..5ab969af 100644
--- a/tests/test_pay.py
+++ b/tests/test_pay.py
@@ -2667,7 +2667,7 @@ def test_setchannel_startup_opts(node_factory, bitcoind):
 def test_channel_spendable(node_factory, bitcoind, anchors):
     """Test that spendable_msat is accurate"""
     sats = 10**6
-    opts = {'plugin': os.path.join(os.getcwd(), 'tests/plugins/hold_invoice.py'), 'holdtime': '30'}
+    opts = {'plugin': os.path.join(os.getcwd(), 'tests/plugins/hold_invoice.py')}
     if anchors is False:
         opts['dev-force-features'] = "-23"
     l1, l2 = node_factory.line_graph(2, fundamount=sats, wait_for_announce=True,
@@ -2693,6 +2693,8 @@ def test_channel_spendable(node_factory, bitcoind, anchors):
     # hold_invoice.py plugin.
     wait_for(lambda: len(l1.rpc.listpeerchannels()['channels'][0]['htlcs']) == 1)
     assert l1.rpc.listpeerchannels()['channels'][0]['spendable_msat'] == Millisatoshi(0)
+    # Tell hold_invoice.py to release hold
+    open(os.path.join(l2.daemon.lightning_dir, TEST_NETWORK, "unhold"), "w").close()
     l1.rpc.waitsendpay(payment_hash, TIMEOUT)
 
     # Make sure l2 thinks it's all over.
@@ -2718,6 +2720,7 @@ def test_channel_spendable(node_factory, bitcoind, anchors):
     # hold_invoice.py plugin.
     wait_for(lambda: len(l2.rpc.listpeerchannels()['channels'][0]['htlcs']) == 1)
     assert l2.rpc.listpeerchannels()['channels'][0]['spendable_msat'] == Millisatoshi(0)
+    open(os.path.join(l1.daemon.lightning_dir, TEST_NETWORK, "unhold"), "w").close()
     l2.rpc.waitsendpay(payment_hash, TIMEOUT)
 
 
@@ -2725,7 +2728,7 @@ def test_channel_receivable(node_factory, bitcoind):
     """Test that receivable_msat is accurate"""
     sats = 10**6
     l1, l2 = node_factory.line_graph(2, fundamount=sats, wait_for_announce=True,
-                                     opts={'plugin': os.path.join(os.getcwd(), 'tests/plugins/hold_invoice.py'), 'holdtime': '30'})
+                                     opts={'plugin': os.path.join(os.getcwd(), 'tests/plugins/hold_invoice.py')})
 
     inv = l2.rpc.invoice('any', 'inv', 'for testing')
     payment_hash = inv['payment_hash']
@@ -2747,6 +2750,7 @@ def test_channel_receivable(node_factory, bitcoind):
     # hold_invoice.py plugin.
     wait_for(lambda: len(l2.rpc.listpeerchannels()['channels'][0]['htlcs']) == 1)
     assert l2.rpc.listpeerchannels()['channels'][0]['receivable_msat'] == Millisatoshi(0)
+    open(os.path.join(l2.daemon.lightning_dir, TEST_NETWORK, "unhold"), "w").close()
     l1.rpc.waitsendpay(payment_hash, TIMEOUT)
 
     # Make sure both think it's all over.
@@ -2773,6 +2777,7 @@ def test_channel_receivable(node_factory, bitcoind):
     # hold_invoice.py plugin.
     wait_for(lambda: len(l1.rpc.listpeerchannels()['channels'][0]['htlcs']) == 1)
     assert l1.rpc.listpeerchannels()['channels'][0]['receivable_msat'] == Millisatoshi(0)
+    open(os.path.join(l1.daemon.lightning_dir, TEST_NETWORK, "unhold"), "w").close()
     l2.rpc.waitsendpay(payment_hash, TIMEOUT)
 
 
@@ -2786,7 +2791,6 @@ def test_channel_spendable_large(node_factory, bitcoind):
         wait_for_announce=True,
         opts={
             'plugin': os.path.join(os.getcwd(), 'tests/plugins/hold_invoice.py'),
-            'holdtime': '30'
         }
     )
 
@@ -2809,6 +2813,7 @@ def test_channel_spendable_large(node_factory, bitcoind):
     # Exact amount should succeed.
     route = l1.rpc.getroute(l2.info['id'], spendable, riskfactor=1, fuzzpercent=0)['route']
     l1.rpc.sendpay(route, payment_hash, payment_secret=inv['payment_secret'])
+    open(os.path.join(l2.daemon.lightning_dir, TEST_NETWORK, "unhold"), "w").close()
     l1.rpc.waitsendpay(payment_hash, TIMEOUT)
 
 
diff --git a/tests/test_plugin.py b/tests/test_plugin.py
index b48d0c03..12a9d6e5 100644
--- a/tests/test_plugin.py
+++ b/tests/test_plugin.py
@@ -17,7 +17,6 @@ from tests.test_wallet import HsmTool, write_all, WAIT_TIMEOUT
 import ast
 import copy
 import json
-import math
 import os
 import pytest
 import random
@@ -663,14 +662,21 @@ def test_invoice_payment_hook(node_factory):
     l2.daemon.wait_for_log('preimage=' + '0' * 64)
 
 
-def test_invoice_payment_hook_hold(node_factory):
+def test_invoice_payment_hook_hold(node_factory, executor):
     """ l1 uses the hold_invoice plugin to delay invoice payment.
     """
-    opts = [{}, {'plugin': os.path.join(os.getcwd(), 'tests/plugins/hold_invoice.py'), 'holdtime': TIMEOUT / 2}]
+    opts = [{}, {'plugin': os.path.join(os.getcwd(), 'tests/plugins/hold_invoice.py')}]
     l1, l2 = node_factory.line_graph(2, opts=opts)
 
     inv1 = l2.rpc.invoice(1230, 'label', 'description', preimage='1' * 64)
-    l1.rpc.pay(inv1['bolt11'])
+
+    # This should block.
+    f = executor.submit(l1.rpc.pay, inv1['bolt11'])
+    time.sleep(5)
+    assert not f.done()
+
+    open(os.path.join(l2.daemon.lightning_dir, TEST_NETWORK, "unhold"), "w").close()
+    f.result(TIMEOUT)
 
 
 @pytest.mark.openchannel('v1')
@@ -4034,8 +4040,7 @@ def test_sql(node_factory, bitcoind):
     l2.rpc.pay(l3.rpc.invoice(amount_msat=12300, label='inv2', description='description')['bolt11'])
 
     # And I need at least one HTLC in-flight so listpeers.channels.htlcs isn't empty:
-    l3.rpc.plugin_start(os.path.join(os.getcwd(), 'tests/plugins/hold_invoice.py'),
-                        holdtime=int(math.sqrt(TIMEOUT) + 1) * 2)
+    l3.rpc.plugin_start(os.path.join(os.getcwd(), 'tests/plugins/hold_invoice.py'))
     inv = l3.rpc.invoice(amount_msat=12300, label='inv3', description='description')
     route = l1.rpc.getroute(l3.info['id'], 12300, 1)['route']
     l1.rpc.sendpay(route, inv['payment_hash'], payment_secret=inv['payment_secret'])
@@ -4103,6 +4108,7 @@ def test_sql(node_factory, bitcoind):
     l3.daemon.wait_for_log("Refreshing channel: {}".format(scid))
 
     # This has to wait for the hold_invoice plugin to let go!
+    open(os.path.join(l3.daemon.lightning_dir, TEST_NETWORK, "unhold"), "w").close()
     txid = only_one(l1.rpc.close(l2.info['id'])['txids'])
     bitcoind.generate_block(13, wait_for_mempool=txid)
     wait_for(lambda: len(l3.rpc.listchannels(source=l1.info['id'])['channels']) == 0)