Added/Updated setUpClass() to create server,images

* Updated these files to add/update setUpClass() to create server and
* images using ComputeIntegrationFixture and to use that in tests
* Removed unused imports
* removed test_add_image_tags() and combined that validation with
* test_add_image_tag() test itself to make use of same image

Change-Id: Ie02c78fe9933374892722a7638c405a30f5269e6
Merge "Added/Updated setUpClass() to create server,images"