core, db: Introduce BaseProfile and DiskProfile

DB and DAL changes: DiskProfileDao to extend ProfileBaseDao

For more information see: http://www.ovirt.org/Features/aggregate_QoS,
http://www.ovirt.org/Features/blkio-support#Profiles

Change-Id: I229af59277b5055453188f002f19046cdd51d63b
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>