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/crypt/test__cryptography_rsa.py b/tests/crypt/test__cryptography_rsa.py
index 41dfc36..dbf07c7 100644
--- a/tests/crypt/test__cryptography_rsa.py
+++ b/tests/crypt/test__cryptography_rsa.py
@@ -60,7 +60,7 @@
 
 
 class TestRSAVerifier(object):
-    def test_verify_bytes_success(self):
+    def test_verify_success(self):
         to_sign = b"foo"
         signer = _cryptography_rsa.RSASigner.from_string(PRIVATE_KEY_BYTES)
         actual_signature = signer.sign(to_sign)
@@ -68,8 +68,8 @@
         verifier = _cryptography_rsa.RSAVerifier.from_string(PUBLIC_KEY_BYTES)
         assert verifier.verify(to_sign, actual_signature)
 
-    def test_verify_text_success(self):
-        to_sign = "foo"
+    def test_verify_unicode_success(self):
+        to_sign = u"foo"
         signer = _cryptography_rsa.RSASigner.from_string(PRIVATE_KEY_BYTES)
         actual_signature = signer.sign(to_sign)
 
diff --git a/tests/crypt/test__python_rsa.py b/tests/crypt/test__python_rsa.py
index 9ef29ee..886ee55 100644
--- a/tests/crypt/test__python_rsa.py
+++ b/tests/crypt/test__python_rsa.py
@@ -12,7 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import io
 import json
 import os
 
@@ -20,6 +19,7 @@
 from pyasn1_modules import pem
 import pytest
 import rsa
+import six
 
 from google.auth import _helpers
 from google.auth.crypt import _python_rsa
@@ -63,7 +63,7 @@
 
 
 class TestRSAVerifier(object):
-    def test_verify_bytes_success(self):
+    def test_verify_success(self):
         to_sign = b"foo"
         signer = _python_rsa.RSASigner.from_string(PRIVATE_KEY_BYTES)
         actual_signature = signer.sign(to_sign)
@@ -71,8 +71,8 @@
         verifier = _python_rsa.RSAVerifier.from_string(PUBLIC_KEY_BYTES)
         assert verifier.verify(to_sign, actual_signature)
 
-    def test_verify_text_success(self):
-        to_sign = "foo"
+    def test_verify_unicode_success(self):
+        to_sign = u"foo"
         signer = _python_rsa.RSASigner.from_string(PRIVATE_KEY_BYTES)
         actual_signature = signer.sign(to_sign)
 
@@ -141,7 +141,7 @@
     def test_from_string_pkcs8_extra_bytes(self):
         key_bytes = PKCS8_KEY_BYTES
         _, pem_bytes = pem.readPemBlocksFromFile(
-            io.StringIO(_helpers.from_bytes(key_bytes)), _python_rsa._PKCS8_MARKER
+            six.StringIO(_helpers.from_bytes(key_bytes)), _python_rsa._PKCS8_MARKER
         )
 
         key_info, remaining = None, "extra"
diff --git a/tests/crypt/test_es256.py b/tests/crypt/test_es256.py
index 720f74c..5bb9050 100644
--- a/tests/crypt/test_es256.py
+++ b/tests/crypt/test_es256.py
@@ -50,7 +50,7 @@
 
 
 class TestES256Verifier(object):
-    def test_verify_bytes_success(self):
+    def test_verify_success(self):
         to_sign = b"foo"
         signer = es256.ES256Signer.from_string(PRIVATE_KEY_BYTES)
         actual_signature = signer.sign(to_sign)
@@ -58,8 +58,8 @@
         verifier = es256.ES256Verifier.from_string(PUBLIC_KEY_BYTES)
         assert verifier.verify(to_sign, actual_signature)
 
-    def test_verify_text_success(self):
-        to_sign = "foo"
+    def test_verify_unicode_success(self):
+        to_sign = u"foo"
         signer = es256.ES256Signer.from_string(PRIVATE_KEY_BYTES)
         actual_signature = signer.sign(to_sign)