Mutable mux test occasionally panics because the server is shut down
before the client goroutine. Fix this by shutting down the client
goroutines before shutting down the server.
We want to be able to update routes without restarting the http
server. mutableRouter is a very thin wrapper around
github.com/gorilla/mux that enables safely switching to a new mux
router without pausing requests.
Soam Vasani