libblkid: check for multi-session CDROMs

libblkid: check for multi-session CDROMs

.. and read last session if probing offset is not specified.

udev uses cdrom_id to get last session offset, so people don't see a
problem with hybrid media (audio+data), but if you execute blkid on
command line (without -O <offset>) then you get I/O errors.

It seems that we can use the same way as kernel filesystem iso9960
driver when session= mount option is not specified ... just use
CDROMMULTISESSION ioctl to get last session offset and probe this last
session rather than all medium.

Signed-off-by: Karel Zak <kzak@redhat.com>