Update device hooks: Added before and after update device hooks.

Bug-Url:https://bugzilla.redhat.com/show_bug.cgi?id=893576
Change-Id: I8fe7f5e6d8291cc227a323b324c977bcd5bc8295
Signed-off-by: Giuseppe Vallarelli <gvallare@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/13972
Reviewed-by: Dan Kenigsberg <danken@redhat.com>