Rename image_client to images_client

Module names of service clients should be <resource name>s_client.py,
and class names also should be <resouce name>sClient.
So this patch renames image_client for matching to the naming rule.

Partially implements blueprint consistent-service-method-names

Change-Id: Id9d8488251d7b1a4642eab08270b787aa6c74050
5 files changed