packaging: add qemu user to cdrom group

Allow to boot VMs from host CD-ROM.

Change-Id: I44d842e7b1df073c33284b51185e29ce0d02a0e0
Bug-Url: https://bugzilla.redhat.com/1082028
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/26541
Reviewed-by: Dan Kenigsberg <danken@redhat.com>