test: Allow pathlib.Path as RPC argument via authproxy

Also, add datadir_path property to TestNode

test/functional/test_framework/authproxy.py

@@ -39,6 +39,7 @@ from http import HTTPStatus
 import http.client
 import json
 import logging
+import pathlib
 import socket
 import time
 import urllib.parse
@@ -62,6 +63,8 @@ class JSONRPCException(Exception):
 def EncodeDecimal(o):
     if isinstance(o, decimal.Decimal):
         return str(o)
+    if isinstance(o, pathlib.Path):
+        return str(o)
     raise TypeError(repr(o) + " is not JSON serializable")
 
 class AuthServiceProxy():