WIP: Subkey docker image (#3183)

* WIP to release subkey im docker

* debug run with publishing

* debug build

* debug build 2

* easier sync

* fix the template

* fix typo

substrate/scripts/docker/subkey.Dockerfile

@@ -0,0 +1,31 @@
+FROM debian:stretch-slim
+
+# metadata
+ARG VCS_REF
+ARG BUILD_DATE
+
+LABEL io.parity.image.authors="devops-team@parity.io" \
+	io.parity.image.vendor="Parity Technologies" \
+	io.parity.image.title="parity/subkey" \
+	io.parity.image.description="Subkey: key generating utility for Substrate." \
+	io.parity.image.source="https://github.com/paritytech/substrate/blob/${VCS_REF}/scripts/docker/subkey.Dockerfile" \
+	io.parity.image.revision="${VCS_REF}" \
+	io.parity.image.created="${BUILD_DATE}" \
+	io.parity.image.documentation="https://github.com/paritytech/substrate/tree/${VCS_REF}/subkey"
+
+# show backtraces
+ENV RUST_BACKTRACE 1
+
+# add user
+RUN useradd -m -u 1000 -U -s /bin/sh -d /subkey subkey
+
+# add subkey binary to docker image
+COPY ./subkey /usr/local/bin
+
+USER subkey
+
+# check if executable works in this container
+RUN /usr/local/bin/subkey --version
+
+ENTRYPOINT ["/usr/local/bin/subkey"]
+