Define volume availability_zones_client as library

Volume availability_zones_clients have good interfaces now,
then this patch makes them as a library.

Partially implements blueprint consistent-service-method-names

Change-Id: I4fc229b113b4f85af22fb3300ae0907dc49f4a73
diff --git a/releasenotes/notes/volume-clients-as-library-9a3444dd63c134b3.yaml b/releasenotes/notes/volume-clients-as-library-9a3444dd63c134b3.yaml
index 101263f..df7e46d 100644
--- a/releasenotes/notes/volume-clients-as-library-9a3444dd63c134b3.yaml
+++ b/releasenotes/notes/volume-clients-as-library-9a3444dd63c134b3.yaml
@@ -6,5 +6,7 @@
     so the other projects can use these modules as stable libraries
     without any maintenance changes.
 
+      * availability_zone_client(v1)
+      * availability_zone_client(v2)
       * extensions_client(v1)
       * extensions_client(v2)