get_info_super: report which other devices are thought to be working/failed.

get_info_super:  report which other devices are thought to be working/failed.

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>