scripted-diff: Use wallets_path and chain_path where possible

Instead of passing the datadir and chain name to os.path.join, just use
the existing properties, which are the same.

-BEGIN VERIFY SCRIPT-
 sed -i --regexp-extended 's|\.datadir, self\.chain, .wallets.|.wallets_path|g' $(git grep -l '\.datadir, self\.chain,')
 sed -i --regexp-extended 's|\.datadir, self\.chain,|.chain_path,|g'            $(git grep -l '\.datadir, self\.chain,')
-END VERIFY SCRIPT-

test/functional/interface_rpc.py

@@ -46,7 +46,7 @@ class RPCInterfaceTest(BitcoinTestFramework):
         command = info['active_commands'][0]
         assert_equal(command['method'], 'getrpcinfo')
         assert_greater_than_or_equal(command['duration'], 0)
-        assert_equal(info['logpath'], os.path.join(self.nodes[0].datadir, self.chain, 'debug.log'))
+        assert_equal(info['logpath'], os.path.join(self.nodes[0].chain_path, 'debug.log'))
 
     def test_batch_request(self):
         self.log.info("Testing basic JSON-RPC batch request...")