Automatic merge from submit-queue

Make kube2sky and skydns docker images cross-platform

ARM tracking issue: #17981
Continues on: #19216

Make it possible to create `kube2sky` and `skydns` docker images for ARM and other architectures too
Build in a container, so `golang` isn't a dependency
I've preserved the original default behaviour:
 - `skydns`: It just compiles with go on host
 - `kube2sky`: Build an image

@brendandburns @dchen1107 @ArtfulCoder @thockin @fgrzadkowski