Convert admin_actions ext tests to unit tests

The tests for the admin_actions API extension (or v3 plugin) are
stubbing out conductor methods, which creates a lot of pain when
compute_api internals are changed.  Convert these tests to unit tests,
checking only that the appropriate compute_api methods are called with
the correct arguments.

Change-Id: I16634efa2397b36afa15b90712bfd678325bc049