Use importlib to take place of imp module

The imp module is deprecated[1] since version 3.4, use importlib to
instead

[1]: https://docs.python.org/3/library/imp.html#imp.reload

Change-Id: I7da97be7403617e1460ae179f7e62dcfa47cdf09

ec2api/tests/unit/test_clients.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import imp
+import importlib
 from unittest import mock
 
 import fixtures
@@ -24,7 +24,7 @@ from ec2api.tests.unit import base
 class ClientsTestCase(base.BaseTestCase):
 
     def setUp(self):
-        imp.reload(clients)
+        importlib.reload(clients)
         super(ClientsTestCase, self).setUp()
 
     @mock.patch.object(clients, '_get_nova_api_version', return_value='2.3')

ec2api/tests/unit/test_context.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import imp
+import importlib
 from unittest import mock
 
 from oslo_config import cfg
@@ -36,7 +36,7 @@ class ContextTestCase(test_base.BaseTestCase):
         clients._admin_session = None
         conf.config(auth_type='fake', group=GROUP_AUTHTOKEN)
 
-        imp.reload(ec2_context)
+        importlib.reload(ec2_context)
         # NOTE(ft): initialize a regular context to populate oslo_context's
         # local storage to prevent admin context to populate it.
         # Used to implicitly validate overwrite=False argument of the call