engine: scheduling manager

Inroducing new clsuter policy arch;
- Handles cluster policy CRUD.
- Handles host selection for a single run/migrate vm iteration.

Detailed description: http://wiki.ovirt.org/Features/oVirtSchedulerAPI

Change-Id: I782f1556f6d955ab644cb437e786e6ef1fa3ea71
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>