use multi-stage docker builds and an autobuild repo

[olix0r]

I think we can replace our dockerize script with a multi-stage build. This will enable us to use an autobuild dockerhub repo.

[olix0r]

Docker for Mac doesn't yet support this (on stable, at least). Once it does, our Dockerfile should probably look something like:

FROM linkerd/rustup-nightly:v1 as nightly-build
RUN rustup update nightly
RUN mkdir -p /linkerd-tcp
COPY . /linkerd-tcp
WORKDIR /linkerd-tcp
RUN cargo build --release

FROM debian:jessie-slim
COPY --from=nightly-build /linkerd-tcp/target/x86_64-unknown-linux-gnu/release/linkerd-tcp /usr/local/bin/
ENTRYPOINT ["/usr/local/bin/linkerd-tcp"]

[olix0r]

Specifically, we need Docker v17.05.0-ce, which is currently a release candidate. Docker for Mac currently uses 17.03.1-ce.