restapi/client: don't use DRF parser for parsing

The DRF parser expect a file-like object containing bytes while
we are passing it a unicode string. The outcome of this is
slumber serialization not working and returning plain bytes
instead of unserialized data.
The fix is trivial and it's just using slumber code for
parsing instead of providing our own.

For reference after making slumber dump exceptions instead of
swallowing here's the root cause:
Traceback (most recent call last): [celery.redirected:235]
File "/venv/lib/python3.5/site-packages/slumber/__init__.py", line 134, in _try_to_serialize_response
  return stype.loads(resp.content.decode(encoding)) [celery.redirected:235]
File "/home/readthedocs/restapi/client.py", line 28, in loads
  return JSONParser().parse(data) [celery.redirected:235]
File "/venv/lib/python3.5/site-packages/rest_framework/parsers.py", line 66, in parse
  return json.load(decoded_stream) [celery.redirected:235]
File "/usr/lib/python3.5/json/__init__.py", line 265, in load
  return loads(fp.read(), [celery.redirected:235]
File "/usr/lib/python3.5/codecs.py", line 493, in read
  newdata = self.stream.read() [celery.redirected:235]
AttributeError: 'str' object has no attribute 'read' [celery.redirected:235]

readthedocs/restapi/client.py

@@ -7,7 +7,6 @@
 import requests
 from django.conf import settings
 from rest_framework.renderers import JSONRenderer
-from rest_framework.parsers import JSONParser
 
 
 log = logging.getLogger(__name__)
@@ -20,13 +19,10 @@
 
 class DrfJsonSerializer(serialize.JsonSerializer):
 
-    """Additional serialization help from the DRF parser/renderer"""
+    """Additional serialization help from the DRF renderer"""
 
     key = 'json-drf'
 
-    def loads(self, data):
-        return JSONParser().parse(data)
-
     def dumps(self, data):
         return JSONRenderer().render(data)
 

readthedocs/rtd_tests/tests/test_restapi_client.py

@@ -0,0 +1,24 @@
+# -*- coding: utf-8 -*-
+from __future__ import (
+    absolute_import, unicode_literals)
+
+from django.test import TestCase
+
+from readthedocs.restapi.client import DrfJsonSerializer
+
+
+class TestDrfJsonSerializer(TestCase):
+    data = {
+       'proper': 'json'
+    }
+    serialized_data = '{"proper":"json"}'
+
+    def test_serializer_loads_json(self):
+        serializer = DrfJsonSerializer()
+        data = serializer.loads(self.serialized_data)
+        self.assertDictEqual(data, self.data)
+
+    def test_serializer_dumps_json(self):
+        serializer = DrfJsonSerializer()
+        serialized_data = serializer.dumps(self.data)
+        self.assertJSONEqual(serialized_data, self.serialized_data)