Use lowercase names for swift/S3 containers

The cinder backup tests are currently failing with the swift s3api
backend because it is invalid for S3 to have uppercase letters in a
bucket name. Use all lowercase instead.

Change-Id: Ifa2f9779af102dc1faf6488332e14aadb8d29bc0
diff --git a/tempest/api/volume/base.py b/tempest/api/volume/base.py
index 53ffe7c..7a08545 100644
--- a/tempest/api/volume/base.py
+++ b/tempest/api/volume/base.py
@@ -202,7 +202,7 @@
                 cont = data_utils.rand_name(
                     prefix=CONF.resource_name_prefix,
                     name=cont_name)
-                kwargs['container'] = cont
+                kwargs['container'] = cont.lower()
 
             self.addCleanup(object_storage.delete_containers,
                             kwargs['container'], container_client,
diff --git a/tempest/api/volume/test_volumes_backup.py b/tempest/api/volume/test_volumes_backup.py
index 2810440..bfe962a 100644
--- a/tempest/api/volume/test_volumes_backup.py
+++ b/tempest/api/volume/test_volumes_backup.py
@@ -82,7 +82,7 @@
         if CONF.volume.backup_driver == "swift":
             kwargs["container"] = data_utils.rand_name(
                 prefix=CONF.resource_name_prefix,
-                name=self.__class__.__name__ + '-Backup-container')
+                name=self.__class__.__name__ + '-backup-container').lower()
         backup = self.create_backup(volume_id=volume['id'], **kwargs)
         self.assertEqual(kwargs["name"], backup['name'])
         waiters.wait_for_volume_resource_status(self.volumes_client,