Images API v2.0 One To Many Image Sharing

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

Refactors the test to add tags.

Refactor to replace all occurrences of admin user by third user
and move getting of tenant id's to the beginning of the file.

Added a needed space between class and the test tags

Change-Id: I2d828a575d7489e806c2f39ad76455f5830264b8
Merge "Images API v2.0 One To Many Image Sharing"