* Some improvment in mesos input plugin,
Removing uneeded statistics prefix for task's metric,
Adding framework id tags into each task's metric,
Adding state (leader/follower) tags to master's metric,
Make sure the slave's metrics are tags with slave
* typo, replacing cpus_total with elected to determine leader
* Remove remaining statistics_ from sample
* using timestamp from mesos as metric timestamp
* change mesos-tasks to mesos_tasks, measurement
* change measurement name in test
* Replace follower by standby
The plugin is able to query a Mesos master and push the metrics, a
blacklist can be configured and a timeout, it's still not used.
Added unit test, might be a good idea to have system test using docker.