Move the object client to tempest.lib

Move the object client to tempest.lib and cleanup the last bits
of code that were required to manage internal-only tempest service
clients.

Change-Id: Ia9aeab78e530c798dfa7b7d6f71e4b3ea3a84b7f
diff --git a/releasenotes/notes/make-object-storage-client-as-stable-interface-d1b07c7e8f17bef6.yaml b/releasenotes/notes/make-object-storage-client-as-stable-interface-d1b07c7e8f17bef6.yaml
new file mode 100644
index 0000000..2bba952
--- /dev/null
+++ b/releasenotes/notes/make-object-storage-client-as-stable-interface-d1b07c7e8f17bef6.yaml
@@ -0,0 +1,11 @@
+---
+features:
+  - |
+    Define below 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.
+
+      * account_client
+      * container_client
+      * object_client