PATCH v2.0/images (cont.).

Implements the following test scenarios:
 - remove additional image property test
 - try update an image by adding status property to it
 - try remove the status property from an image
 - try replace the status property of an image.

Fixes the assertion in remove additional test property test.

Change-Id: Ib3b42a308377b0c12a3c15a20bdbb5779213b32a
Merge "PATCH v2.0/images (cont.)."