Consolidate dockerfiles and add docs for development

This will reduce the number of files that need to be managed and dependencies that need updated at the same time.

docker/Dockerfile

@@ -0,0 +1,37 @@
+# Run vmpooler in a Docker container!  Configuration can either be embedded
+# and built within the current working directory, or stored in a
+# VMPOOLER_CONFIG environment value and passed to the Docker daemon.
+#
+# BUILD:
+#   docker build -t vmpooler .
+#
+# RUN:
+#   docker run -e VMPOOLER_CONFIG -p 80:4567 -it vmpooler
+
+FROM amd64/jruby:9.3.6-jdk
+
+LABEL org.opencontainers.image.description "VMPooler plus all known providers"
+
+ENV DEBIAN_FRONTEND=noninteractive
+ENV LOGFILE=/dev/stdout
+ENV RACK_ENV=production
+
+RUN apt-get update -qq && \
+    apt-get upgrade -y && \
+    apt-get install -y --no-install-recommends make git netbase && \
+    apt-get clean autoclean && \
+    apt-get autoremove -y && \
+    rm -rf /var/lib/apt/lists/*
+
+RUN gem install bundler
+
+COPY ./docker-entrypoint.sh /usr/local/bin/
+
+RUN chmod +x /usr/local/bin/docker-entrypoint.sh
+
+COPY ./Gemfile* ./
+
+RUN bundle config set --local jobs 3 && \
+    bundle install
+
+ENTRYPOINT ["docker-entrypoint.sh"]