contrib: Dockerfile: add a base stage
contrib: Dockerfile: add a base stage

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

mikebrow/containerd,crosbymichael/containerd,dmcgowan/containerd,containerd/containerd,mikebrow/containerd,thaJeztah/containerd,dmcgowan/containerd,vdemeester/containerd,crosbymichael/containerd,estesp/containerd,vdemeester/containerd,containerd/containerd,thaJeztah/containerd,estesp/containerd