Ping event should not trigger builds

While reviewing @bparees sample application I found out that he was triggering build with ping event, which is abiously wrong, I must have overlooked that case. So this PR extendeds integration tests with that test case and fixes it.
@bparees @mfojtik review pls.
Couple lines before we're rejecting anything other than ping and push events so far. But I've changed it to reflect what we're accepting.