polkadot collator builder (#740)

* dockerfiles: polkadot-collator_builder.Containerfile and docs

* dockerfiles: optimize test dockerfile

docker/test-parachain-collator.dockerfile

@@ -1,23 +1,8 @@
-FROM rust:buster as builder
+# This file is sourced from https://github.com/paritytech/polkadot/blob/master/scripts/dockerfiles/polkadot/polkadot_builder.Dockerfile
+FROM docker.io/paritytech/ci-linux:production as builder
 
-RUN apt-get update && apt-get install time clang libclang-dev llvm -y
-RUN rustup toolchain install nightly
-RUN rustup target add wasm32-unknown-unknown --toolchain nightly
-RUN command -v wasm-gc || cargo +nightly install --git https://github.com/alexcrichton/wasm-gc --force
-
-WORKDIR /paritytech/cumulus
-
-# Ideally, we could just do something like `COPY . .`, but that doesn't work:
-# it busts the cache every time non-source files like inject_bootnodes.sh change,
-# as well as when non-`.dockerignore`'d transient files (*.log and friends)
-# show up. There is no way to exclude particular files, or write a negative
-# rule, using Docker's COPY syntax, which derives from go's filepath.Match rules.
-#
-# We can't combine these into a single big COPY operation like
-# `COPY collator consensus network runtime test Cargo.* .`, because in that case
-# docker will copy the _contents_ of each directory into the image workdir,
-# not the actual directory. We're stuck just enumerating them.
-COPY . .
+WORKDIR /cumulus
+COPY . /cumulus
 
 RUN cargo build --release --locked -p polkadot-collator