Define volume services_client as library

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

Partially implements blueprint consistent-service-method-names

Change-Id: I1b4f38033830ce7bed24d97e73072fd7a2f03f09
diff --git a/releasenotes/notes/volume-clients-as-library-9a3444dd63c134b3.yaml b/releasenotes/notes/volume-clients-as-library-9a3444dd63c134b3.yaml
index b1fe74a..6a4fc2b 100644
--- a/releasenotes/notes/volume-clients-as-library-9a3444dd63c134b3.yaml
+++ b/releasenotes/notes/volume-clients-as-library-9a3444dd63c134b3.yaml
@@ -12,3 +12,5 @@
       * extensions_client(v2)
       * hosts_client(v1)
       * hosts_client(v2)
+      * services_client(v1)
+      * services_client(v2)