fix: add back python 2.7 for gcloud usage only (#892)

* fix: add back python 2.7 for gcloud

* fix: fix setup and tests

* fix: add enum34 for python 2.7

* fix: add app engine app and fix noxfile

* fix: move test_app_engine.py

* fix: fix downscoped

* fix: fix downscoped

* fix: remove py2 from classifiers
diff --git a/tests/test_identity_pool.py b/tests/test_identity_pool.py
index e90e288..87e343b 100644
--- a/tests/test_identity_pool.py
+++ b/tests/test_identity_pool.py
@@ -13,13 +13,13 @@
 # limitations under the License.
 
 import datetime
-import http.client
 import json
 import os
-import urllib
 
 import mock
 import pytest
+from six.moves import http_client
+from six.moves import urllib
 
 from google.auth import _helpers
 from google.auth import exceptions
@@ -92,7 +92,7 @@
 
     @classmethod
     def make_mock_request(
-        cls, token_status=http.client.OK, token_data=None, *extra_requests
+        cls, token_status=http_client.OK, token_data=None, *extra_requests
     ):
         responses = []
         responses.append(cls.make_mock_response(token_status, token_data))
@@ -218,14 +218,14 @@
         # service account impersonation request.
         requests = []
         if credential_data:
-            requests.append((http.client.OK, credential_data))
+            requests.append((http_client.OK, credential_data))
 
         token_request_index = len(requests)
-        requests.append((http.client.OK, token_response))
+        requests.append((http_client.OK, token_response))
 
         if service_account_impersonation_url:
             impersonation_request_index = len(requests)
-            requests.append((http.client.OK, impersonation_response))
+            requests.append((http_client.OK, impersonation_response))
 
         request = cls.make_mock_request(*[el for req in requests for el in req])