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__helpers.py b/tests/test__helpers.py
index 906cf12..0c0bad2 100644
--- a/tests/test__helpers.py
+++ b/tests/test__helpers.py
@@ -13,9 +13,9 @@
 # limitations under the License.
 
 import datetime
-import urllib
 
 import pytest
+from six.moves import urllib
 
 from google.auth import _helpers
 
@@ -65,8 +65,8 @@
     assert _helpers.to_bytes(value) == value
 
 
-def test_to_bytes_with_text():
-    value = "string-val"
+def test_to_bytes_with_unicode():
+    value = u"string-val"
     encoded_value = b"string-val"
     assert _helpers.to_bytes(value) == encoded_value
 
@@ -76,14 +76,14 @@
         _helpers.to_bytes(object())
 
 
-def test_from_bytes_with_text():
-    value = "bytes-val"
+def test_from_bytes_with_unicode():
+    value = u"bytes-val"
     assert _helpers.from_bytes(value) == value
 
 
 def test_from_bytes_with_bytes():
     value = b"string-val"
-    decoded_value = "string-val"
+    decoded_value = u"string-val"
     assert _helpers.from_bytes(value) == decoded_value