Move config drive tests into misc policy actions file

This commit does 3 things:
  1a) Corrects the "config_drive" tests by aligning the
      tests with the nova policy documentation [0] which
      states that "config_drive" is to added the response
      body of showing a server or listing servers with details
      if policy enforcement passes.
  1b) Consequently, 2 tests are added: 1 for show and 1 for
      list with details.
  2) Moves both tests into the misc policy actions file to
     increase gate stability and decrease gate run time.

The number of calls to create_test_server() should be minimized
for RBAC testing because we don't do too much modification to the
resources that are created -- only what's necessary to trigger the
API action corresponding to the RBAC policy under test. Further,
minimizing such calls reduces the risk of spinning up too many servers
concurrently in our gates: the source of various gate failures as
limited resources lead to server faults being raised.

[0] https://github.com/openstack/nova/blob/master/nova/policies/config_drive.py

Change-Id: If54fce795c2289b097b617cad7268dc9a3d9cf1c
Partial-Bug: #1699415
3 files changed