433262 - WebSocket / Advanced close use cases

+ Improved test case handling of frame reading (to prevent future
  false failures)
+ Improved AbstractWebSocketConnection handling of close -> disconnect
  to only trigger on successful write (or failure) of close frame flush
  attempt.
+ Flusher close on all forms of disconnect, even half-closed.
433512 Jetty throws RuntimeException when webapp compiled with jdk8 -parameters