Don't match cdroms on any bus

We can't install on cdroms. If ID_CDROM is 1, skip that device.
Otherwise, PXE booted systems with (storage|ovirt)_init specified
and no other specifiers may pick a CDROM, as it shows up on the
ata bus as a disk. Be more specific.

Change-Id: I0e7d39e36027addd8612f2768939c7e4f0766e7e
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1163688
Signed-off-by: Ryan Barry <rbarry@redhat.com>