Wait briefly after calling ListenAndServe{TLS} to see if it errors.

An unfortunate effect of using net/http ListenAndServe and
ListenAndServeTLS is that you don't get early errors like "permission
denied" and "address already in use"--they happen later which means they
appear only in the meek-server log, not in the tor log. Here we apply a
hack to hold on for a fraction of a second to see if the call errors,
hopefully long enough to catch most of such errors.