dm integrity: recalculate checksums on creation

When using external metadata device and internal hash, recalculate the
checksums when the device is created - so that dm-integrity doesn't
have to overwrite the device.  The superblock stores the last position
when the recalculation ended, so that it is properly restarted.

Integrity tags that haven't been recalculated yet are ignored.

Also bump the target version.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>