SIGHUPs that happen during a check run are ignored

[volfco]

I've noticed this bug. When you have a long running check, if the application sends a SIGHUP to reload the config during the execution phase; the SIGHUB is ignored.

This looks to be the result of the following line: https://github.com/DataDog/dd-agent/blob/33afda662aade99500f454b33f208e8289818d7b/agent.py#L353

The above line should be moved above self.collector.run so if a SIGHUP happens during the check it's caught by the reload code.