Add tests for create grant when no user

There were no tests that show what happens when you create a grant
(PUT /v3/projects/{project_id}/users/{user_id}/roles/{role_id} and
/v3/domains/{domain_id}/...) for a user that doesn't exist. The
server returns a 404 Not Found for the user.

bp no-check-id

Change-Id: I8b6e9c6c667d523a645472a227c60d2d65fe8d57
Merge "Add tests for create grant when no user"