Use GOVENDOREXPERIMENT=1 from the start

[luxas]

Use godep with GOVENDOREXPERMIENT set to 1.
Store files in vendor/ (makes godep used only when adding/removing deps)
Also, require go1.6+ for building

[dlorenc]

I think we can close this. The initial work uses godep and go 1.6, so GOVENDOREXPERMIENT=1 by default :)