Fix a bug - collector mandatory fields were used instead of optional

Change-Id: I91efa2403341f65b4e843c276e52cc32c028b614
Signed-off-by: Martin Pavlasek <mpavlase@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/33321
Reviewed-by: Martin Sivák <msivak@redhat.com>
Reviewed-by: Adam Litke <alitke@redhat.com>