restapi: disk entity export to glance

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=990962
Change-Id: If351d209d7828f0d59926bb98da9317567976d41
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
backend: add ActionGroup to access image domains

Change-Id: Ifbff053962ae1dceef51c7d8ff356fcf527aa5e2
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>