More precise solution to #771

[mattrjacobs]

Instead of try-catching all hook errors, follow this pattern:

• For a hook at the beginning of an event, assume that a thrown exception replaces the surrounded event. For example, onExecutionStart() throwing implies that the run()/construct() method does not get run, but it looks from the outside as if it threw an exception.
• For a hook at the end of an event, there is no such ability to replace a value, so just try-catch and log.

This allows for hooks to influence behavior without having to subclass HystrixCommand. I've also added a unit test that asserts state is properly maintained when hooks throw Exceptions

[cloudbees-pull-request-builder]

NetflixOSS » Hystrix » Hystrix-pull-requests #113 FAILURE
Looks like there's a problem with this pull request

[cloudbees-pull-request-builder]

NetflixOSS » Hystrix » Hystrix-pull-requests #114 SUCCESS
This pull request looks good