Images API v2.0 Image Discovery Shared Images Owned By User

Implements image discovery of shared images owned by user:
 - added a new test scenario.
 - refactored fixtures.
 - reverted changes on the image fixtures and made it a separate PR.
 - improved naming of variables.

Change-Id: I36b5fd4c8ebc9c3b0f7a85468911f4493969f687
Merge "Images API v2.0 Image Discovery Shared Images Owned By User"