Do away with partial request completions and all the associated
complexity. Individual object requests no longer need to be completed
in order -- when the last one becomes ready, we complete the entire
higher level request all at once.
This also wraps up the conversion to a state machine model and
eliminates the recursion described in commit 6d69bb536bac ("rbd:
prevent kernel stack blow up on rbd map").
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
7114edac35