Moved tests for server._action_rebuild

Move tests to separate class as a preparation for code
deduplication.

This work continues in https://review.openstack.org/34556

bp nova-tests-code-duplication

Change-Id: I985232fa0a9b2d5b73034047b06138a8a3d7e390
Code dedup in tests for server._action_rebuild

Externed common parts to setUp():
- request body
- request object
- test image UUID
- test image URL
These parts were equal in the most part of the methods.

bp nova-tests-code-duplication

Change-Id: Ie29dd090075915a4065ee395b4e50fc178f72f3b
Merge "Moved tests for server._action_rebuild"
Merge "Code dedup in tests for server._action_rebuild"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp