Create: add support for RAID0 layouts.

Create: add support for RAID0 layouts.

Since Linux 5.4 a layout is needed for RAID0 arrays with
varying device sizes.
This patch makes the layout of an array visible (via --examine)
and sets the layout on newly created arrays.
--layout=dangerous
can be used to avoid setting a layout so that they array
can be used on older kernels.

Tested-by: dann frazier <dann.frazier@canonical.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>