Remove duplicate appends to image list.

The BaseImageTest class method create_image() already adds created
images to the list of created images. Created images don't need to be
manually appended to the class image tracking list created_images. This
removes all the duplicate appends for tests that use the base class
create_image().

Change-Id: Id99e7ed9a88e513172b1962993dd21bd5feea02f
Merge "Remove duplicate appends to image list."