Jmxfetch

This pull request merges the changes made to use the new jmxfetch ( https://github.com/DataDog/jmxfetch )

This new connector is living in its own process and is collecting periodically metrics from the jmx server. 
It then sends these metrics to the agent using DogStatsD.

This pull request:
- Gets rid of the previous checks
- Calls the new JMXFetch when the agent starts if some jmx checks are configured
- Tweak Dogstatsd and the info page so the info page displays informations about the jmx checks