[qa] py2: Unfiddle strings into bytes explicitly in ZMQ RPC test

Extracted from bitcoin/bitcoin#7853
commit faa41ee204124da19dcf1e5b8a3aef1e216bf5e6

qa/rpc-tests/test_framework/util.py

@@ -1,6 +1,8 @@
 # Copyright (c) 2014 The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+
 #
 # Helpful routines for regression testing
 #
@@ -9,6 +11,8 @@
 import os
 import sys
 
+from binascii import hexlify, unhexlify
+from base64 import b64encode
 from decimal import Decimal, ROUND_DOWN
 import json
 import random
@@ -32,6 +36,15 @@ def check_json_precision():
     if satoshis != 2000000000000003:
         raise RuntimeError("JSON encode/decode loses precision")
 
+def bytes_to_hex_str(byte_str):
+    return hexlify(byte_str).decode('ascii')
+
+def hex_str_to_bytes(hex_str):
+    return unhexlify(hex_str.encode('ascii'))
+
+def str_to_b64str(string):
+    return b64encode(string.encode('utf-8')).decode('ascii')
+
 def sync_blocks(rpc_connections, wait=1):
     """
     Wait until everybody has the same block count