Remove update_private

Remove update_private

This fields doesn't work any more as ->getinfo_super clears the info
structure at an awkward time.  So get rid of it and do it differently.

The issue is that the metadata handler cannot tell if the uuid it has
was randomly generated or explicitly requested, except on the first
call.
And we don't want to accept explicit requests for IMSM.
So when it was auto-generated, make it look distinctive by having the
same int copied in all 4 positions.  If someone requests a uuid like
that, I guess they get away with it.

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