`NoopPing`: Remove `UnsupportedProtocolErr`.

This avoids log noise if the proprietary pinger is disabled.
Makefile: Explicitly prepend `GOPATH` to commands.
Merge pull request #99 from mozilla-services/bug/makefile-log-noise

Set `GOPATH` explicitly, squelch proprietary ping failures
Add /status/ endpoint to websocket client mux

This is useful for monitoring the push endpoint separately from the
update endpoint.
Merge branch 'dev' of github.com:mozilla-services/pushgo into dev