Handling InterruptedExceptions in the HystrixMetricsStreamServlet

Some environments like spring boots embedded Tomcat interrupt the worker threads on shutdown. Interupting a thread is the Java way to politely ask it to gracefully stop doing long running things. Since serving an event stream is a long running thing, we should stop sending the stream and stop polling, whenever an InterruptedException occures.
Merge pull request #253 from BGehrels/master

Handling InterruptedExceptions in the HystrixMetricsStreamServlet