reports:Fixed bug in br18-chart vms with known OS vs. unknown

Fixed bug in br18, ovirt 3.3, where chart vms with known OS vs.
unknown OS.
All OS were defined as Known.

Change-Id: Icce38b6deff21b3b2684d283f8c46bc098eb5f79
Signed-off-by: Shirly Radco <sradco@redhat.com>
Related-To:  https://bugzilla.redhat.com/1059268