[NC-887] release docker image (#71)

Provide a release grade Docker image

fix NC-887
use OpenJDK 8 slim docker image and integrated builder step
Replace the previous unused dockerfile with also some integrated documentation
Automatic building of the image and push to DockerHub will be done in a new Jenkins job

Dockerfile

@@ -1,13 +1,42 @@
-# Base Alpine Linux based image with OpenJDK JRE only
-#FROM openjdk:8-jre-alpine
-FROM openjdk:8-jdk
+# Pantheon release grade Docker image
+#
+# What is this image for ?
+#   This image is for using Pantheon within Docker for any purpose, test, dev, production.
+#   The Docker file integrates two steps, first the build with a JDK and then the runnning image with a JRE.
+#   Then you don't need a JDK installed locally to build Pantheon, just run the docker build
+#   command and once the image is created you can use it as if you were using a regular Patheon binary.
+#
+# How to use this image:
+#
+#   first build it (use the name and tag you like) :
+#
+#   docker build -t mypantheon:myTag .
+#
+#   then run pantheon:
+#   Either as a simple node with sync on mainnet with a volume for data (keeps the database between runs) and that's all:
+#
+#   docker run -d --mount source=pantheon_database,target=/opt/pantheon/database --name myPantheon mypantheon:myTag
+#
+#   or as a simple node with sync on mainnet with a volume for data (keeps the database between runs) and  HTTP/WS RPC access :
+#
+#   docker run -d --mount source=pantheon_database,target=/opt/pantheon/database \
+#   --name myPantheon -p 8545:8545 -p 8546:8546 mypantheon:myTag \
+#   --rpc-enabled --rpc-listen=0.0.0.0:8545 --rpc-cors-origins=mydomain.tld \
+#   --ws-enabled -ws-listen=0.0.0.0:8546
 
-# copy application (with libraries inside)
-ADD build/install/pantheon /opt/pantheon/
-ADD integration-tests/src/test/resources/tech/pegasys/pantheon/tests/cluster/docker/geth/genesis.json /opt/pantheon/genesis.json
+# builder temporary image with JDK
+FROM openjdk:8-jdk-slim as builder
+# copy all pantheon source to the image
+COPY . /tmp/pantheon
+WORKDIR /tmp/pantheon
+# build the distribution
+RUN ./gradlew installDist
 
+# final image with only jre
+FROM openjdk:8-jre-slim
+# copy application from builder image
+COPY --from=builder /tmp/pantheon/build/install/pantheon /opt/pantheon/
 # List Exposed Ports
-EXPOSE 8084 8545 30303 30303/udp
-
+EXPOSE 8546 8545 30303
 # specify default command
 ENTRYPOINT ["/opt/pantheon/bin/pantheon"]