PATCH v2.0/images

Update a specified image's property - Smoke Test.

Tested update the name of an image.
Refactored fixtures.
Addressed reviewer comment - removed unused rest client in fixtures.

Reordered the import as per reviewer comment.
Added explicit assertion messages for all assertions as per reviewer comments.
Added a short description for each of the methods in the fixtures.
Made some small changes in the fixtures.

Added explicit assertion messages for other assertions as per reviewer comment.
Moved the constant MSG to fixtures.

Moved the msg constant to fixtures setUpClass.
Fixed line continuation and import issues.

Removed the custom assertion message.
Added a new line.

Change-Id: Iec757d087a0696416ef8e5668a498440bf07d802
Merge "PATCH v2.0/images"