Disable cinder backup import/export test

There is a bug in Cinder (#1455043) and backups are incorrectly imported
into the DB, current Tempest test is based on that incorrect behavior,
so once we fix that in Cinder current tempest backup import/export test
fails.

So we have a cyclic dependency because Cinder fix will not work with
current Tempest test, and Tempest fix will not work with current Cinder
code.

To break this cyclic dependency we need to temporary disable backup
import/export test in Tempest in order to merge the fix in Cinder and
then we can merge the Tempest fix that reenables the test.

Related Cinder change is: Ia42ba73e9078d993c63f8e16308151ad11721ea9

Related-Bug: #1455043
Related-Bug: #1476416
Change-Id: Id7ab6e174c1fe85772477f03059c4f457c5c8b17

tempest/api/volume/admin/test_volumes_backup.py

@@ -14,6 +14,7 @@
 #    under the License.
 
 from oslo_log import log as logging
+from tempest_lib import decorators
 
 from tempest.api.volume import base
 from tempest.common.utils import data_utils
@@ -79,6 +80,7 @@ class VolumesBackupsV2Test(base.BaseVolumeAdminTest):
         self.admin_volume_client.wait_for_volume_status(
             restore['volume_id'], 'available')
 
+    @decorators.skip_because(bug='1455043')
     @test.idempotent_id('a99c54a1-dd80-4724-8a13-13bf58d4068d')
     def test_volume_backup_export_import(self):
         # Create backup