message: [build] Update cluster-test docker file to common pattern
  This allows to reuse layers from previous builds when building cluster test
  Closes:
  Approved by: snakech
diff: -FROM debian:buster AS builder
  -## To use http/https proxy while building, use:
  -## docker build --build-arg https_proxy=http:
  -RUN apt-get update && apt-get install -y cmake curl clang git libssl-dev pkg-config
  -RUN curl --proto '=https' --tlsv1.2 -sSf "https://sh.rustup.rs" | sh -s -- -y --default-toolchain none
  +FROM debian:buster AS toolchain
  +
  +# To use http/https proxy while building, use:
  +# docker build --build-arg https_proxy=http://fwdproxy:8080 --build-arg http_proxy=http://fwdproxy:8080
  +
  +RUN apt-get update && apt-get install -y cmake curl clang git
  +
  +RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --default-toolchain none
  ENV PATH "$PATH:/root/.cargo/bin"
  +
  WORKDIR /libra
  COPY rust-toolchain /libra/rust-toolchain
  RUN rustup install $(cat rust-toolchain)
  +
  +FROM toolchain AS builder
  +
  COPY . /libra
  RUN ./docker/build-common.sh
  