restapi: missing vms link under affinity groups

Change-Id: Ia913bee64669db435be49463821ae68fe61978be
Bug-Url: https://bugzilla.redhat.com/1128461
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>
(cherry picked from commit b8feb5728bf72b50df230af5915c3c1544ccb3ab)