imsm: FIX: Disable automatic metadata rollback for broken reshape

imsm: FIX: Disable automatic metadata rollback for broken reshape

mdmon cannot rollback metadata changes automatically.
It can break reshape process in the way that in case of reshape break
user will not be able to deal with broken reshape due to lack of information
about reshape geometry.

mdadm (process that invokes reshape) doesn't make any rollback to allow
for user action. mdmon should not do this either unless it knows for sure
it is save. such knowledge is not available for automatic rollback.

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