Remove StoragePool.getImageDomainsList().

Avoid code duplication.

Related to BZ#905038.

Change-Id: I225fa7a58e1fabb844cc883938e94df39d2a8ae2
Signed-off-by: Eduardo <ewarszaw@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/12927
Tested-by: Elad Ben Aharon <eladba1990@gmail.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>