blkid: retport block size of a filesystem

blkid: retport block size of a filesystem

This patch extends libblkid, so that it reports filesystem block size.

When blkid returns a specific number in the BLOCK_SIZE attribute, it
guarantees that all the bios submitted by the filesystem are aligned on
this boundary.

We need this because when we want to enable dm-integrity or dm-writecache
on an existing filesystem, we need to know filesystem block size, so that
dm-integrity or dm-writecache is initialized with matching block size.

We could always use block size 512 for dm-integrity and dm-writecache, but
that would cause metadata overhead and performance degradation. On the
other hand, if we used block size 4096, it would fail if the filesystem
has smaller blocksize.

[kzak@redhat.com: - move vfat BLOCK_SIZE to probing function
		  - remove unwanted debug fprintf from ZFS prober]

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