hsm: move domainStateCallback to HSM

It seems that the garbage collector is not fast enough to clear the
callback per-pool that we added in commit:

 7e30615 sp: update domain links on state change

This different approach will allow us to add only one callback (per
HSM) and forward the event to the current connected pools.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1086210
Relates-To: https://bugzilla.redhat.com/show_bug.cgi?id=1093924
Change-Id: I7509aced432dfa77dbec727d57f507d1a9c550b7
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27478
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>