test: Use TestNode *_path properties where possible

Seems odd to place the burden on test writers to hardcode the chain or
datadir path for the nodes under test.

test/functional/feature_filelock.py

@@ -3,7 +3,6 @@
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Check that it's not possible to start a second bitcoind instance using the same datadir or wallet."""
-import os
 import random
 import string
 
@@ -24,7 +23,7 @@ class FilelockTest(BitcoinTestFramework):
         self.nodes[0].wait_for_rpc_connection()
 
     def run_test(self):
-        datadir = os.path.join(self.nodes[0].datadir, self.chain)
+        datadir = self.nodes[0].chain_path
         self.log.info(f"Using datadir {datadir}")
 
         self.log.info("Check that we can't start a second bitcoind instance using the same datadir")
@@ -35,7 +34,7 @@ class FilelockTest(BitcoinTestFramework):
             def check_wallet_filelock(descriptors):
                 wallet_name = ''.join([random.choice(string.ascii_lowercase) for _ in range(6)])
                 self.nodes[0].createwallet(wallet_name=wallet_name, descriptors=descriptors)
-                wallet_dir = os.path.join(datadir, 'wallets')
+                wallet_dir = self.nodes[0].wallets_path
                 self.log.info("Check that we can't start a second bitcoind instance using the same wallet")
                 if descriptors:
                     expected_msg = f"Error: SQLiteDatabase: Unable to obtain an exclusive lock on the database, is it being used by another instance of {self.config['environment']['PACKAGE_NAME']}?"