clean reproducable builds

[Dieterbe]

needed for raintank-docker, and basically just needed period.
go 1.6 will adopt go vendoring (see https://docs.google.com/document/d/1Bz5-UB7g2uPBdOx-rw5t9MxJwkfpx90cqG9AFL0JAYo/edit) but that's only part of the solution: we also need to be able to elegantly put, and maintain packages in the vendor directory.
i tried using git submodules, but it's too much work to specify everything manually
https://github.com/kr/vexp looks like it solves it, but it's yet another 3rd party tool.
godep now supports it, see https://github.com/tools/godep#go-15-vendor-experiment so this seems interesting. i've always found godep complicated and cumbersome (or at least how it's used with grafana) but maybe now it's different.

i wonder if with the advent of 1.6 this will also become a solved problem, but i don't think so.

[Dieterbe]

Think I'll try glide for this

[Dieterbe]

see #197