Add multistage Dockerfile

[Vanuan]

This would enable automatic builds on Docker Hub

[GordonTheTurtle]

Please sign your commits following these rules: https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work The easiest way to do this is to amend the last commit:

$ git clone -b "multistage-dockerfile" git@github.com:Vanuan/infrakit.git somewhere
$ cd somewhere
$ git commit --amend -s --no-edit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[codecov[bot]]

Codecov Report

Merging #909 into master will decrease coverage by 0.06%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #909      +/-   ##
==========================================
- Coverage   48.42%   48.36%   -0.07%     
==========================================
  Files          84       84              
  Lines        7859     7859              
==========================================
- Hits         3806     3801       -5     
- Misses       3743     3747       +4     
- Partials      310      311       +1

Impacted Files	Coverage Δ
pkg/rpc/mux/server.go	42.7% <0%> (-5.21%)	:arrow_down:

---

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[Vanuan]

@thebsdbox Is this a legitimate failure?

[thebsdbox]

@vanuan looks ok. I’ll double check and merge shorty! 🙂

[thebsdbox]

@Vanuan Not sure if I'd recommend bumping the FROM to more recent golang-alpine given the vulnerability news last week.

[Vanuan]

@thebsdbox What do you mean? I didn't bump anything, I've taken what's already there in https://github.com/docker/infrakit/blob/master/dockerfiles/Dockerfile.build

[thebsdbox]

No worries, I’ll bump the golang base image in another PR.

[thebsdbox]

Thanks @Vanuan 👍🏻