block/rbd: Propagate errors to open and create methods Completes the conversion to Error started in commit 015a103^..d5124c0. Cc: Josh Durgin <josh.durgin@inktank.com> Signed-off-by: Markus Armbruster <armbru@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>