Allow Grow_continue for whole container as well as single array.

Allow Grow_continue for whole container as well as single array.

Some grow operations must be applied to a whole container.  These
are performed one array at a time, so only one array appears to
be reshaping.

When re-assembling such an array, we need to make sure that
when the reshape finished, we move on to the next array.

So require metadata to set ->reshape_active = 2 in that case,
and use reshape_container to complete the reshape.

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