fsck: improve whole-disk check, detect stacked devices

fsck: improve whole-disk check, detect stacked devices

The current heuristic for conversion from partition to whole-disk
is based on device names. It's pretty poor. This patch replaces this
code with blkid_devno_to_wholedisk(). This solution is based on
/sys FS and it works for arbitrary partitioned devices.

The another problem is the way how fsck determines stacked devices.
The current code checks device name for "md" prefix only. It does not
care about DM, dm-ccypt, and so on. This patch uses
/sys/block/.../slaves/, but it does not fully resolves dependencies
between all devices. The method is simple -- fsck does not check
stacked devices in parallel with any other device.

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