Enable create array with write journal (--write-journal DEVICE).

Enable create array with write journal (--write-journal DEVICE).

Specify the write journal device with --write-journal DEVICE

./mdadm --create -f /dev/md0 --assume-clean -c 32 --raid-devices=4 --level=5 /dev/sd[c-f] --write-journal /dev/sdb1
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.

Only one journal device is allowed. If multiple --write-journal
are given, mdadm will use the first and ignore others

./mdadm --create -f /dev/md0 --assume-clean -c 32 --raid-devices=4 --level=5 /dev/sd[c-f] --write-journal /dev/sdb1 --write-journal /dev/sdx
mdadm: Please specify only one journal device for the array.
mdadm: Ignoring --write-journal /dev/sdx...
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: NeilBrown <neilb@suse.com>