tune2fs: rebuild and checksum directories when necessary

tune2fs: rebuild and checksum directories when necessary

Since all the metadata checksums depend on the fs UUID, tune2fs must
be able to rewrite the checksums of _all_ metadata.  It's not that
hard to add in the bits to resize the directory block structures at
the same time.

[ Merged in fix from Zheng Liu where ctx.errcode wasn't getting
  cleared in rewrite_directory(). ]

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>