tests: fix mnemonic handling following seed changes

### tests/__init__.py
@@ -27,10 +27,8 @@
     # Mnemonic used in identity tests
     'identity': 'alcohol woman abuse must during monitor noble \
 actual mixed trade anger aisle',
-    # Used to ensure the on-device cached mnemonic is changed to an
-    # otherwise unused mnemonic for tests that set a custom mnemonic/seed
-    'invalidatecache': 'abandon abandon abandon abandon abandon abandon abandon \
-    abandon abandon abandon abandon cactus'
+    # Ensure the on-device cached mnemonic is reset before the test
+    'reset': 'reset'
 })
 
 # Seeds used in tests

### tests/conftest.py
@@ -57,16 +57,18 @@ def _create_api(self):
 
     def set_mnemonic(self, mnemonic):
         """Set the current jade mnemonic (with caching)."""
-        if mnemonic != self.current_mnemonic:
-            # reset the jade
-            rslt = self.jade.clean_reset()
-            assert rslt is True
+        do_reset = mnemonic == mnemonics.reset
+        if do_reset or mnemonic != self.current_mnemonic:
             # mnemonic differs from the one currently set: change and remember it
-            rslt = self.jade.set_mnemonic(mnemonic)
+            rslt = self.jade.clean_reset()
             assert rslt is True
-            self.current_mnemonic = mnemonic
-            # invalidate seed
-            self.current_seed = None
+            if do_reset:
+                self.current_mnemonic = None  # invalidate mnemonic
+            else:
+                rslt = self.jade.set_mnemonic(mnemonic)
+                assert rslt is True
+                self.current_mnemonic = mnemonic
+            self.current_seed = None  # invalidate seed
         time.sleep(1)
 
     def set_seed(self, seed):
@@ -77,8 +79,7 @@ def set_seed(self, seed):
         # set seed
         rslt = self.jade.set_seed(bytes.fromhex(seed))
         assert rslt is True
-        # invalidate mnemonic
-        self.current_mnemonic = None
+        self.current_mnemonic = None  # invalidate mnemonic
         time.sleep(1)
 
     def disconnect(self):
@@ -210,8 +211,8 @@ def mnemonic(request):
        @pytest.mark.mnemonic(mnemonics.singlesig)
     """
     s = _get_test_seed(request.node)
-    if s == '':  # no seed, set mnemonic
-        m = _get_test_mnemonic(request.node) or mnemonics.default
-        get_jade_config().jade.set_mnemonic(m)
-    else:  # if there is seed ignore mnemonic and set seed
+    if s:
         get_jade_config().set_seed(s)
+    else:
+        m = _get_test_mnemonic(request.node) or mnemonics.default
+        get_jade_config().set_mnemonic(m)

### tests/rpc/test_address.py
@@ -10,7 +10,7 @@ def test_get_greenaddress_receive_address(jade, test_case):
         assert rslt == expected
 
 
-@pytest.mark.mnemonic(mnemonics.invalidatecache)
+@pytest.mark.mnemonic(mnemonics.reset)
 @pytest.mark.seed(seeds.singlesig)
 @with_test_cases('tests/rpc/data/address/single_sig_addr.json')
 def test_get_singlesig_receive_address(jade, mnemonic, test_case):

### tests/rpc/test_descriptor.py
@@ -57,7 +57,7 @@ def test_miniscript_descriptor_registration(jade, test_case):
     _test_miniscript_descriptor_registration(jade, test_case)
 
 
-@pytest.mark.mnemonic(mnemonics.invalidatecache)
+@pytest.mark.mnemonic(mnemonics.reset)
 @pytest.mark.seed(seeds.singlesig)
 @with_test_cases('tests/rpc/data/descriptor/descriptor_ss_*.json')
 def test_miniscript_descriptor_registration_ss(jade, test_case):

### tests/rpc/test_mnemonic.py
@@ -108,8 +108,8 @@ def _set_wallet(jade, mnemonic=mnemonics.default, passphrase=None):
     return reply['result']
 
 
-@pytest.mark.mnemonic(mnemonics.invalidatecache)
-def test_12word_mnemonic(jade):
+@pytest.mark.mnemonic(mnemonics.reset)
+def test_12word_mnemonic(jade, mnemonic):
     # Short sanity-test of 12-word mnemonic
     rslt = jade.set_mnemonic(TEST_MNEMONIC_12)
     assert rslt is True
@@ -120,8 +120,8 @@ def test_12word_mnemonic(jade):
     assert rslt == '38SBTKLCNKVvQh1jPpbkAbXa3gtRJEh9Ud'
 
 
-@pytest.mark.mnemonic(mnemonics.invalidatecache)
-def test_mnemonic_import(jade):
+@pytest.mark.mnemonic(mnemonics.reset)
+def test_mnemonic_import(jade, mnemonic):
     # Check the mnemonic unique prefixes expands to the same mnemonic/wallet
     # as when giving the full mnemonic words (test for qr-scanning prefixes)
     # as the unambiguous prefixes are expanded to the full words.  orc -> orchard
@@ -158,8 +158,8 @@ def test_mnemonic_import(jade):
     assert xpub_root2 == xpub_root0
 
 
-@pytest.mark.mnemonic(mnemonics.invalidatecache)
-def test_mnemonic_import_bad(jade):
+@pytest.mark.mnemonic(mnemonics.reset)
+def test_mnemonic_import_bad(jade, mnemonic):
     # Check importing invalid mnemonics
     bad_mnemonics = [
         # mnemonic phrase
@@ -189,8 +189,8 @@ def test_mnemonic_import_bad(jade):
         assert any(m in message for m in expected), message
 
 
-@pytest.mark.mnemonic(mnemonics.invalidatecache)
-def test_passphrase(jade):
+@pytest.mark.mnemonic(mnemonics.reset)
+def test_passphrase(jade, mnemonic):
     # Set mnemonic with/without a passphrase, and get root xpub
     xpub0 = _set_wallet(jade.jade, passphrase=None)
     xpub1 = _set_wallet(jade.jade, passphrase='Passphrase1')

### tests/rpc/test_multisig.py
@@ -340,7 +340,7 @@ def test_generic_multisig_matches_ga_signatures_liquid(jade, test_case):
         _check_tx_signatures(jade, ga_msig, rslt)
 
 
-@pytest.mark.mnemonic(mnemonics.invalidatecache)
+@pytest.mark.mnemonic(mnemonics.reset)
 @pytest.mark.seed(seeds.singlesig)
 @with_test_cases('tests/rpc/data/multisig/multisig_reg_ss_*.json')
 def test_generic_multisig_ss_signer(jade, mnemonic, test_case):

### tests/rpc/test_pinserver.py
@@ -24,16 +24,12 @@ def test_set_pinserver(jade):
     assert rslt
 
 
-@pytest.mark.mnemonic(mnemonics.invalidatecache)
-def test_handshake(jade):
+@pytest.mark.mnemonic(mnemonics.reset)
+def test_handshake(jade, mnemonic):
     """
     Pinserver handshake test - note this is tightly coupled to the dedicated
     test handler in the hardware code (main/process/debug_handshake.c)
     """
-    # Reset the jade
-    rslt = jade.clean_reset()
-    assert rslt is True
-    get_jade_config().current_mnemonic = None
     # First override the hww pinserver pubkey to match the local test key
     TEST_URL = 'https://this.is.a.test.url.com'
     TEST_ONION = 'http://we.dont.know.our.onion.but.this.string.is.about.the.right.size'
@@ -147,8 +143,8 @@ def test_handshake(jade):
     assert reply2['result'] is True
 
 
-@pytest.mark.mnemonic(mnemonics.invalidatecache)
-def test_handshake_bad_server(jade):
+@pytest.mark.mnemonic(mnemonics.reset)
+def test_handshake_bad_server(jade, mnemonic):
     """
     Pinserver handshake test - set the hww back to the default/production
     authentication data - this should then fail with 'bad-sig' when we sign