imsm: close removed drive fd.

imsm: close removed drive fd.

When member drive fails, managemon prepares metadata update and adds
the drive to disk_mgmt_list with DISK_REMOVE flag. It fills only
minor and major. It is enough to recognize the device later.

Monitor thread while processing this update will remove the drive from
super only if it is a spare. It never removes failed member from
disks list. As a result, it still keeps opened descriptor to
non-existing device.

If removed drive is not a spare fill fd in disk_cfg structure
(prepared by managemon), monitor will close fd during freeing it.

Also set this drive fd to -1 in super to avoid double closing because
monitor will close the fd (if needed) while replacing removed drive
in array.

Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@intel.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>