Improve specs for command line option mocks in Python tests

When trying to mock the objects generated by our command line options wrappers, we use specs. e.g.

    mock_options = Mock(spec_set=['cluster', 'disable_all_hooks', 'duration', 'filename', 'grouping',
      'hosts', 'percentage', 'post_drain_script', 'reason', 'unsafe_hosts_filename', 'verbosity'])

These specs are duplicating strings defined in the command verbs and nouns. We should instead look to introspect our commands and pull the list of acceptable options from there - and use that to define our specs.