mke2fs: skip zeroing journal blocks

mke2fs: skip zeroing journal blocks

Add the ability to skip zeroing journal blocks on disk.  This can
significantly speed up mke2fs with large journals.  At worst the
uninitialized journal is only a very short-term risk (if at all),
because the journal will be overwritten on any new filesystem as
soon as any significant amount of data is written to disk, and
the new journal TID would need to match the offset/TID of an old
commit block still left on disk.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>