Move object storage bulk_middleware_client to lib interface

object storage bulk_middleware_client is stable now and good to be moved
as stable library interface.

Partially implements blueprint consistent-service-method-names

Change-Id: I6b44fb9a692b947baadbe049b2f7d31e4ab51035

releasenotes/notes/migrate-object-storage-as-stable-interface-42014c7b43ecb254.yaml

@@ -0,0 +1,8 @@
+---
+features:
+  - |
+    Define object storage service clients as libraries
+    Add new service clients to the library interface so the other projects can use these modules as stable libraries without
+    any maintenance changes.
+
+      * bulk_middleware_client

tempest/services/object_storage/__init__.py

@@ -12,9 +12,9 @@
 # License for the specific language governing permissions and limitations under
 # the License.
 
-from tempest.services.object_storage.account_client import AccountClient
-from tempest.services.object_storage.bulk_middleware_client import \
+from tempest.lib.services.object_storage.bulk_middleware_client import \
     BulkMiddlewareClient
+from tempest.services.object_storage.account_client import AccountClient
 from tempest.services.object_storage.capabilities_client import \
     CapabilitiesClient
 from tempest.services.object_storage.container_client import ContainerClient

tempest/tests/lib/services/object_storage/test_bulk_middleware_client.py

@@ -12,7 +12,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from tempest.services.object_storage import bulk_middleware_client
+from tempest.lib.services.object_storage import bulk_middleware_client
 from tempest.tests.lib import fake_auth_provider
 from tempest.tests.lib.services import base