core: OVFs that aren't stored on any domain should be stored on all

When the VM/Template has no non shareable image disks, its OVF file won't be
stored on any domain. This patches changes this behavior by storing
those OVFs on all the domains.

Change-Id: Iaeecc6c4526800656315842384d83830fdf0b72b
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1138134
Signed-off-by: Liron Aravot <laravot@redhat.com>