Rubinius metrics meet influxdb II

Hi guys @brixen and @jemc I just took advance of my timezone difference to start the second part of the RBX InfluxDB series, please fell free to ad/remove anything.

Awesome work with docker @jemc  \o/
Isn't it more common to use "If you are **on** Mac OS X" instead of "If you are **in** Mac OS X"?