DDF: Fix assorted typos and do some reformatting.

..because it is more fun when new patches are harder to apply to old version :-)

Signed-off-by: NeilBrown <neilb@suse.de>
DDF: mark missing-on-assembly device properly.

As well as removing from the array we really should mark
it is 'failed', and mark the array as degraded.

Signed-off-by: NeilBrown <neilb@suse.de>
DDF: guard against ->pdnum being negative.

It is conceivable that ->pdnum could be -1, though only if
the metadata is corrupt.
We should be careful not to use it if it is.

Also remove an assignment for pdnum to ->container_member.
This is never used and cannot possibly mean anything.

Signed-off-by: NeilBrown <neilb@suse.de>
DDF: fix possible mdmon crash when updating metadata.

Testing 'c' and then using 'vdc' assumes that the two are in sync,
but sometimes they aren't.
Testing 'vdc' is safer.
This avoids a crash in some cases when failing/removing/added devices
to a DDF.

Signed-off-by: NeilBrown <neilb@suse.de>
DDF: Don't fail compare_super_ddf due to re-configure changes.

It is possible that one device has seem some reconfig but the other
hasn't.  In that case  they are still the "same" DDF, even though
one might be older.  Such age will be detected by 'seq' differences.

If A is new and B is old, then it is import that
  mdadm -I B
  mdadm -I A

doesn't get confused because A has the same uuid as B, but compare_super fails.

So: if the seq numbers are different, then just accept as two
different superblocks.
If they are the same, then look to copy data from new to old.

Signed-off-by: NeilBrown <neilb@suse.de>
systemd: various fixes for boot with container-arrays.

1/ Add systemd shutdown script to ensure DDF and IMSM are
   clean before we actually shutdown

2/ Get udev to tell systemd to run the mdmon@mdXXX.service
   units when a member array appears.

   If we boot off a member array (with dracut at least),
   the mdmon started in the initramfs will lose track of
   /sys etc, so we need to restart it.
   systemd will try to forget about it too (but not actually
   kill it because we said not to do this).
   Having udev tell it to start it will allow a new mdmon to
   run which can see /sys, and systemd will know about it.

3/ Always use --offroot and --takeover when starting mdmon with
   systemd
   --offroot is needed else shutdown will hang.
   --takeover is needed incase an mdmon was started earlier
   (e.g. in initramfs).
   Neither hurt if they aren't actually needed.

Signed-off-by: NeilBrown <neilb@suse.de>