libblkid: avoid probing CDs for RAID

libblkid: avoid probing CDs for RAID

RAID probing of CD/DVD can yield errors because of well-known problem
in reading the end of the disk with some disk/drive combinations.
Borrow CD detection method from udev and skip the RAID tests for
these devices.

[kzak@redhat.com: - check for linux/cdrom.h in ./configure
                  - add #ifdef around the ioctl call
                  - call the ioctl for block devices only]

Signed-off-by: Mark Colclough <m.s.colclough@bham.ac.uk>
Signed-off-by: Karel Zak <kzak@redhat.com>