Replace parse_strtime with datetime.strptime

This change switches the use of parse_strtime to datetime.strptime since
oslo.utils parse_strtime simply calls strptime from the datetime library[0],
which keystone already uses.

[0] https://github.com/openstack/oslo.utils/blob/master/oslo_utils/timeutils.py#L97

Change-Id: I9d428d16bfe5ed83a9ff441725c293576a11e09d

keystone/tests/unit/external/test_timeutils.py

@@ -12,8 +12,6 @@
 
 import datetime
 
-from oslo_utils import timeutils
-
 import keystone.tests.unit as tests
 
 
@@ -21,13 +19,13 @@ class TestTimeUtils(tests.BaseTestCase):
 
     def test_parsing_date_strings_returns_a_datetime(self):
         example_date_str = '2015-09-23T04:45:37.196621Z'
-        dt = timeutils.parse_strtime(example_date_str, fmt=tests.TIME_FORMAT)
+        dt = datetime.datetime.strptime(example_date_str, tests.TIME_FORMAT)
         self.assertIsInstance(dt, datetime.datetime)
 
     def test_parsing_invalid_date_strings_raises_a_ValueError(self):
         example_date_str = ''
         simple_format = '%Y'
         self.assertRaises(ValueError,
-                          timeutils.parse_strtime,
+                          datetime.datetime.strptime,
                           example_date_str,
-                          fmt=simple_format)
+                          simple_format)

keystone/tests/unit/test_v3.py

@@ -12,11 +12,11 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import datetime
 import uuid
 
 import oslo_context.context
 from oslo_serialization import jsonutils
-from oslo_utils import timeutils
 from six.moves import http_client
 from testtools import matchers
 import webtest
@@ -549,7 +549,7 @@ class RestfulTestCase(unit.SQLDriverOverrides, rest.RestfulTestCase,
 
     def assertValidISO8601ExtendedFormatDatetime(self, dt):
         try:
-            return timeutils.parse_strtime(dt, fmt=TIME_FORMAT)
+            return datetime.datetime.strptime(dt, TIME_FORMAT)
         except Exception:
             msg = '%s is not a valid ISO 8601 extended format date time.' % dt
             raise AssertionError(msg)