osd_types: s/stashed/rollback_info_completed and set on create

Originally, this flag indicated that the object had already been stashed and
that therefore recording subsequent changes is unecessary.  We want to set it
on create() as well since operations like [create, writefull] should not need
to stash the object.

Fixes: #8625
Signed-off-by: Samuel Just <sam.just@inktank.com>