Bug fix to UFS/FFS superblock integrity checks when reading a superblock.

Older versions of growfs(8) failed to correctly update fs_dsize.
Filesystems that have been grown fail the test for fs_dsize's correct
value. For now we exclude the fs_dsize test from the requirements.

Reported by: Edward Tomasz Napiera
Tested by: Edward Tomasz Napiera
Tested by: Peter Holm
MFC after: 1 month (with 076002f24d35)
Differential Revision: https://reviews.freebsd.org/D35219