engine: set QoS href under profile

* Add a qurey to fetch all qos entities by type
* For disk, cpu and vnic profile, fetch all qos objects (if needed),
and set the DataCenter, inorder to map it to
correct path (/DataCenter/<dc_id>/qoss/<qos_id>/)

Change-Id: Ib345485d9d64d3adf28c2ea61a17c0cc0c828abb
Bug-Url: https://bugzilla.redhat.com/1078863
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>