To accurately detect when an array has been split and is now being
recombined, we need to track which other devices each thinks is
working.
We should never include a device in an array if it thinks that the
primary device has failed.
This patch just allows get_info_super to return a list of devices
and whether they are thought to be working or not.
Signed-off-by: NeilBrown <neilb@suse.de>