Improve Addition of Java to Docker Image

Previously, the Docker file added a bunch of utilities and downloaded the
version of Java directly in the image that was eventually created.  This left
a bunch of unnecessary and potentially vulnerable packages on the image that
was used in production.  This change makes the build a multi-stage build and
ensures that the network utilities required for downloading only exist on a
disposed stage.

In addition to the change to a multi-stage build, this change also swaps from
the Pivotal Distribution of OpenJDK to BellSoft Liberica.

Signed-off-by: Ben Hale <bhale@vmware.com>

Dockerfile

@@ -1,19 +1,36 @@
-FROM ubuntu:bionic
+ARG DOWNLOAD_URI=https://github.com/bell-sw/Liberica/releases/download/11.0.8+10/bellsoft-jre11.0.8+10-linux-amd64.tar.gz
+ARG SHA256=b4cb31162ff6d7926dd09e21551fa745fa3ae1758c25148b48dadcf78ab0c24c
+
+# Download and verify file
+# Args: $DOWNLOAD_URI, $SHA256
+FROM ubuntu:bionic AS retrieve
 
 RUN apt-get update && apt-get install --no-install-recommends -y \
     ca-certificates \
     curl \
-    netcat \
-    wget \
-    fontconfig \
  && rm -rf /var/lib/apt/lists/*
 
-ENV JAVA_HOME /opt/openjdk
+ARG DOWNLOAD_URI
+RUN curl -L \
+    $DOWNLOAD_URI \
+    > download.tar.gz
+
+ARG SHA256
+RUN echo "${SHA256} download.tar.gz" | sha256sum -c - 2>&1
+
+# Install File
+FROM ubuntu:bionic
+
+ENV JAVA_HOME /usr/lib/jvm/jre
 ENV PATH $JAVA_HOME/bin:$PATH
 
 COPY wait-for-it.sh /wait-for-it.sh
 RUN chmod +x /wait-for-it.sh
 
-RUN mkdir -p /opt/openjdk \
- && cd /opt/openjdk \
- && curl https://java-buildpack.cloudfoundry.org/openjdk/bionic/x86_64/openjdk-1.8.0_192.tar.gz | tar xz
+COPY --from=retrieve download.tar.gz /tmp/download.tar.gz
+
+RUN mkdir -p /usr/lib/jvm \
+ && tar xzf /tmp/download.tar.gz -C /usr/lib/jvm \
+ && ln -s /usr/lib/jvm/* /usr/lib/jvm/jre \
+ && rm /tmp/download.tar.gz
+