core: scheduling: VM Affinity Group filter and weight module

Filter filters out hosts that doen't comply with affinity rules.
Weight module uses filter logic to give high weight to hosts that would
have filtered out.

Added by deafult to all cluster policies.

For more information please refer
to: http://www.ovirt.org/Features/VM-Affinity

Change-Id: I9716523591852635496799412ad387850d6c372d
Bug-Url: https://bugzilla.redhat.com/1036638
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>