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/wallet_backwards_compatibility.py

@@ -74,8 +74,8 @@ class BackwardsCompatibilityTest(BitcoinTestFramework):
 
     def nodes_wallet_dir(self, node):
         if node.version < 170000:
-            return os.path.join(node.datadir, "regtest")
-        return os.path.join(node.datadir, "regtest/wallets")
+            return node.chain_path
+        return node.wallets_path
 
     def run_test(self):
         node_miner = self.nodes[0]
@@ -157,10 +157,10 @@ class BackwardsCompatibilityTest(BitcoinTestFramework):
         assert info['keypoolsize'] == 0
 
         # Unload wallets and copy to older nodes:
-        node_master_wallets_dir = os.path.join(node_master.datadir, "regtest/wallets")
-        node_v19_wallets_dir = os.path.join(node_v19.datadir, "regtest/wallets")
-        node_v17_wallets_dir = os.path.join(node_v17.datadir, "regtest/wallets")
-        node_v16_wallets_dir = os.path.join(node_v16.datadir, "regtest")
+        node_master_wallets_dir = node_master.wallets_path
+        node_v19_wallets_dir = node_v19.wallets_path
+        node_v17_wallets_dir = node_v17.wallets_path
+        node_v16_wallets_dir = node_v16.chain_path
         node_master.unloadwallet("w1")
         node_master.unloadwallet("w2")
         node_master.unloadwallet("w3")