imsm: FIX: Perform first metadata update for container operation

imsm: FIX: Perform first metadata update for container operation

Meta data was not updated due to the following problems:
1.disk index < 0 was treated as invalid, but this is spare device
2. disk index greater than currently used disks is correct also
3. newmap pointer has to be refreshed for second map copy operation
4. size calculation has to be guarded for shrinking operation

Signed-off-by: Adam Kwolek <adam.kwolek@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>