vm: rename method for clarity

rename _getGuestStatus for clarity and
to reduce the clashing with _getGuestStats.

Change-Id: I1b8ef022dce13ab0f4e1e8f5de994d11942d8bfd
Signed-off-by: Francesco Romani <fromani@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/28223
Reviewed-by: Michal Skrivanek <michal.skrivanek@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>