engine : A user with PowerUserRole|NetworkUser on DC doesn't see own diskless templates when creating new VM

A user with PowerUserRole|NetworkUser on DC doesn't see
own diskless templates when creating new VM based on
this diskless template.

Change-Id: Ia13631aa82204fbbabf95f6ef4e3c4d082abc2b1
Bug-Url: https://bugzilla.redhat.com/906817
Signed-off-by: Ravi Nori <rnori@redhat.com>