Rename compute images_client to compute_images_client

We have two image client one from nova and another from glance.
Nove- cls.images_client
glance- cls.image_client
Both names are very confusing to use or debug.

This commit rename the nova images_client to compute_images_client
in Manager and in test cases too.

Partially implements blueprint consistent-service-method-names

Change-Id: I5d67a8ef91b522b5d96011e3039f784caec76b03
20 files changed