Images API v2.0 One-To-One Image Sharing Test

Implements one-to-one image sharing test:
 - added new test scenario 'one-to-one image sharing'
 - refactored fixtures
 - reverted changes on the image fixtures and made it a separate PR.
 - improve naming of variables.

Refactors to add tags to the test.

Change-Id: Ib179e364f7a3dd67796d29cc4b0216ca0b2a12bf
Merge "Images API v2.0 One-To-One Image Sharing Test"