nfsd: make openstateids hold references to their openowners

Change it so that only openstateids hold persistent references to
openowners. References can still be held by compounds in progress.

With this, we can get rid of NFS4_OO_NEW. It's possible that we
will create a new openowner in the process of doing the open, but
something later fails. In the meantime, another task could find
that openowner and start using it on a successful open. If that
occurs we don't necessarily want to tear it down, just put the
reference that the failing compound holds.

Signed-off-by: Jeff Layton <jlayton@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>