core: Adding affinity groups command and queries

queries: get by cluster id and get by vm id
commands: create update and delete

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

Change-Id: I5251d0ee6ff2a719394cdb5ebec7b63e0ae37e3b
Bug-Url: https://bugzilla.redhat.com/1036638
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>