extension of IncrementalRemove to store location (path-id) of removed device

extension of IncrementalRemove to store location (path-id) of removed device

If the disk is taken out from its port this port information is
lost. Only udev rule can provide us with this information, and then we
have to store it somehow. This patch adds writing 'cookie' file in
/dev/.mdadm/failed-slots directory in form of file named with value of
f<path-id> containing the metadata type and uuid of the array (or
container) that the device was a member of.  The uuid is in exactly
the same format as in the mapfile.

FAILED_SLOTS_DIR constant has been added to hold the location of
cookie files.

Signed-off-by: Przemyslaw Czarnowski <przemyslaw.hawrylewicz.czarnowski@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>