py3: decode bytes for json.loads()

In py 3.5 json.loads requires to have string as input, all bytes must be
decoded.

Note: python 3.6 supports bytes for json.loads()

https://fedorahosted.org/freeipa/ticket/4985

Reviewed-By: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Jan Cholasta <jcholast@redhat.com>

ipalib/rpc.py

@@ -1101,7 +1101,8 @@ class JSONServerProxy(object):
         )
 
         try:
-            response = json_decode_binary(json.loads(response.decode('ascii')))
+            response = json_decode_binary(
+                json.loads(response.decode('utf-8')))
         except ValueError as e:
             raise JSONError(error=str(e))