Add detection mechanism which will allow to check whether a path to a
block device is a physical CDROM drive. This will be useful once we will
need to pass it to hypervisors.

The linux implementation uses an ioctl to do the detection, while the
fallback uses a simple string prefix match.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>