Port server actions unittests to V3 API Part 2

Ports the server actions unittests to test the V3 API.
This mostly involved CamelCase to camel_case changes
and adpating the URLs to point to the V3 API instead of
the V2 API.

It also includes
- Fixing a bug in the admin_password extension picked up by
  the tests where bad request data is not always handled properly
- Generate image ref urls that point to glance api rather than
  the nova api. This fits in with the decision to not port the images
  extension to the V3 API which is implemented here:
  https://review.openstack.org/#/c/40565/
- Moves admin password related tests to the admin password unittests
  test file as this functionality has been moved out from core.

Partially implements blueprint v3-api-unittests

Change-Id: I58b4c0103c824898183fca890c74c3c1cbe19633
Merge "Port server actions unittests to V3 API Part 2"