common: Introduce profiles package & Disk Profile

- Introduce ProfileBase abstract class
- Introduce ProfileType
- Introduce DiskProfile (implements ProfileBase)

For more information see http://www.ovirt.org/Features/aggregate_QoS

Change-Id: I1a9af22277b50554531511002f19046c0051d8ff
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>