Add ausearch and semange customisations to SELinux plug-in

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>
Rename Plugin.get_cmd_dir() to get_cmd_path()

The method to retrieve the path into which a plug-in's collected
command output returns a path as a string rather than a directory
object.

Make this clear by renaming the method to 'get_cmd_path()'.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>