Port keystonemiddleware to Python 3

On Python 3, memcache returns data as Unicode, but the hmac module
expects bytes. Encode data to UTF-8.

Fix also DisableModuleFixture.clear_module() on Python 3. dict.keys() is
now an iterator on Python 3: create a list because sys.modules is
modified in the loop body.

Closes-Bug: #1449423
Change-Id: Id4805c01b0127a3a86235a7d1a4bb3863b51a6b6

keystonemiddleware/auth_token/_cache.py

@@ -268,6 +268,8 @@ class TokenCache(object):
         if serialized is None:
             return None
 
+        if isinstance(serialized, six.text_type):
+            serialized = serialized.encode('utf8')
         data = self._deserialize(serialized, context)
 
         # Note that _INVALID_INDICATOR and (data, expires) are the only

keystonemiddleware/tests/unit/utils.py

@@ -108,7 +108,7 @@ class DisableModuleFixture(fixtures.Fixture):
 
     def clear_module(self):
         cleared_modules = {}
-        for fullname in sys.modules.keys():
+        for fullname in list(sys.modules.keys()):
             if (fullname == self.module or
                     fullname.startswith(self.module + '.')):
                 cleared_modules[fullname] = sys.modules.pop(fullname)