Hystrix.reset() now shuts down the HystrixTimer

- the HystrixTimer can be shutdown via an interrupt (which Hystrix.reset uses)
- the HystrixTimer will correctly restart the thread if it is used again after a reset

https://github.com/Netflix/Hystrix/issues/109
Merge pull request #111 from benjchristensen/issue-109

Hystrix.reset() now shuts down the HystrixTimer