Add os-create-backup compute RBAC test

Add RBAC test for creating a server backup, providing coverage for the
policy action: "os_compute_api:os-create-backup".

This patch also:
  - Removes unnecessary setUp from ServerActionsV216RbacTest
    since it does a rebuild server in case something bad
    happened to the server -- but there is only 1 test case
    in the class.
  - Use data_utils.rand_name to create a fake host name for
    evacuate server test to further randomize host name to
    guarantee 404 is thrown which is the desired outcome.

Change-Id: Ia5f95deb7b9495345db50c0569885a17b22984f6
Depends-On: Ib97e65cca468a09bbeaf68fcfe0e8192674a481e
2 files changed