Failing unit tests for timeouts on HystrixCommands not causing thread interruptions

This is a PR slightly modified from #354.  Thanks @aadeon for the contribution, I can replicate your failure.

cc @benjchristensen, it seems like we need a way to explicitly control thread interruption of the Observable underlying a HystrixCommand.  Can you take a look and see if there's a workaround in Hystrix, or if corresponding RxJava changes are needed?