FIX: imsm: OROM does not recognize degraded arrays (V2)

FIX: imsm: OROM does not recognize degraded arrays (V2)

Defect description:
When we create an redundant array in mdadm and then degrade it
by disk removing, Option ROM and Windows OS does not detect any array.
Reason:
Metadata created and updated after degrading array is not compatible
with IMSM standard.

This patch synchronizes the metadata according IMSM requirements.
Following inconsistencies have been fixed:
- reset all fields in imsm_dev during creation to avoid random values
- init dev status during creation to proper state
- not reset CONFIGURED_DISK flag when disk is missing
- add ":0" suffix to the serial number for missing/failed disks
- update medatada signature after takeover operation
- mark map state as degraded after raid0->raid10 takeover

Note:
Patch reworked after Dan Willams review.

Signed-off-by: Krzysztof Wojcik <krzysztof.wojcik@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>