Feature/minimal output

[dcarbone]

Hi,

First thanks for writing this package, it works very well and saved us having to write something ourselves :)

That said, we have our health checks handled by Consul, and unfortunately having a changing health message even with a non-change in health state causes a new entry in the Consul Raft log, which has recently started giving us grief.

To that end, I have added a new minimal flag which, if passed, will zero-out the message portion of the status.

I have also updated the package to use go dep and updated some bits of the code and test packages to use the newer docker package.

Let me know if you see any issues!

[CLAassistant]

All committers have signed the CLA.