Add an all-in-one Dockerfile

Built off the [jruby](https://hub.docker.com/_/jruby/) `Dockerfile`,
it installs gem requirements via `bundler`, installs and runs a
`redis-server`, imports the current working directory, starts
`vmpooler`, and tails the logfile.

Creating a `vmpooler.yaml` configuration file in the current working
directory and running the following provides a development environment:

```
docker build -t vmpooler . && docker run -p 80:4567 -it vmpooler
```

Dockerfile

@@ -0,0 +1,22 @@
+FROM jruby:1.7-jdk
+
+RUN mkdir -p /var/lib/vmpooler
+WORKDIR /var/lib/vmpooler
+
+ADD Gemfile /var/lib/vmpooler
+ADD Gemfile.lock /var/lib/vmpooler
+RUN bundle install --system
+
+RUN ln -s /opt/jruby/bin/jruby /usr/bin/jruby
+
+RUN echo "deb http://httpredir.debian.org/debian jessie main" >/etc/apt/sources.list.d/jessie-main.list
+RUN apt-get update
+RUN apt-get install -y redis-server
+
+COPY . /var/lib/vmpooler
+
+ENTRYPOINT \
+    /etc/init.d/redis-server start \
+    && /var/lib/vmpooler/scripts/vmpooler_init.sh start \
+    && while [ ! -f /var/log/vmpooler.log ]; do sleep 1; done ; \
+    tail -f /var/log/vmpooler.log