Add docker-compose and dockerfile to support it

This commit adds a docker-compose file and a dockerfile to build vmpooler and install it from source.

docker/Dockerfile_local

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+# 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 jruby:9.1-jdk
+
+COPY docker/docker-entrypoint.sh /usr/local/bin/
+COPY ./ ./
+
+ENV RACK_ENV=production
+
+RUN bundle && gem build vmpooler.gemspec && gem install vmpooler*.gem && \
+      chmod +x /usr/local/bin/docker-entrypoint.sh
+
+ENTRYPOINT ["docker-entrypoint.sh"]

docker/docker-compose.yml

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+# For local development run with a dummy provider
+version: '3.2'
+services:
+  vmpooler:
+    build:
+      context: ../
+      dockerfile: docker/Dockerfile_local
+    volumes:
+      - type: bind
+        source: ${PWD}/vmpooler.yaml
+        target: /etc/vmpooler/vmpooler.yaml
+    ports:
+      - "4567:4567"
+    networks:
+      - redis-net
+    environment:
+      - VMPOOLER_DEBUG=true # for use of dummy auth
+      - VMPOOLER_CONFIG_FILE=/etc/vmpooler/vmpooler.yaml
+      - REDIS_SERVER=redis
+    image: vmpooler-local
+    depends_on:
+      - redis
+  redis:
+    image: redis
+    ports:
+      - "6379:6379"
+    networks:
+      - redis-net
+
+networks:
+  redis-net: