engine : NPE is raised when accessing via REST /groups url

A NPE exception is raised when querying for user
groups using restapi with filtered=true

GetAllDbGroups does not have the corresponding
query class it was named GetAllAdGroupsQuery

Change-Id: Iff5562bdb130530b952053e72d4446c0019812aa
Bug-Url: https://bugzilla.redhat.com/1099831
Signed-off-by: Ravi Nori <rnori@redhat.com>