Use common "waiters.wait_for_image_status" function everywhere

In Tempest we have the waiters.wait_for_image_status function that
is already used in some places. So this commit replaces the use of the
wait_for_image_status method defined in the images_client.py file with
the use of the waiters.wait_for_image_status function.

Change-Id: If42cfbfa1f7dae5af276e80f38f6294ced00ac5b
diff --git a/tempest/tests/common/test_waiters.py b/tempest/tests/common/test_waiters.py
index 492bdca..a56f837 100644
--- a/tempest/tests/common/test_waiters.py
+++ b/tempest/tests/common/test_waiters.py
@@ -38,8 +38,7 @@
         # Ensure waiter returns before build_timeout
         self.assertTrue((end_time - start_time) < 10)
 
-    @mock.patch('time.sleep')
-    def test_wait_for_image_status_timeout(self, mock_sleep):
+    def test_wait_for_image_status_timeout(self):
         time_mock = self.patch('time.time')
         time_mock.side_effect = utils.generate_timeout_series(1)
 
@@ -47,15 +46,12 @@
         self.assertRaises(exceptions.TimeoutException,
                           waiters.wait_for_image_status,
                           self.client, 'fake_image_id', 'active')
-        mock_sleep.assert_called_once_with(1)
 
-    @mock.patch('time.sleep')
-    def test_wait_for_image_status_error_on_image_create(self, mock_sleep):
+    def test_wait_for_image_status_error_on_image_create(self):
         self.client.show_image.return_value = ({'status': 'ERROR'})
         self.assertRaises(exceptions.AddImageException,
                           waiters.wait_for_image_status,
                           self.client, 'fake_image_id', 'active')
-        mock_sleep.assert_called_once_with(1)
 
     @mock.patch.object(time, 'sleep')
     def test_wait_for_volume_status_error_restoring(self, mock_sleep):