Remove Josh as per his request since he is no longer the upstream RBD
tech lead. Add myself as the maintainer since I am the current RBD tech
lead.

Signed-off-by: Jason Dillaman <dillaman@redhat.com>
Reviewed-by: Josh Durgin <jdurgin@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>