fix(web-server): close webserver after running

When we're done running the tests and all clients are disconnected,
we should stop the http server. This way another karma instance (or
anything else for that matter) may reuse the port later.
fix(web-server): detach listeners after running

Remove listeners from the global process and the webserver when we're
done. The EmitterWrapper can be used to wrap any EventEmitter and
remembers the listeners that were via the wrappers addListener/on
function. Then the wrapper's removeAllListeners function can be used
to remove the wrapper's listeners, leaving the listeners that were
added directly to the unwrapped emitter attached.
Merge pull request #928 from jpommerening/fix-close-http-port-at-exit

Stop the WebServer after running tests