RethinkDB running from docker

This is currently at the proof of concept level and should not 
be considered anything other than a toy.

This shows how to restart a docker container on its hook invocations
with new cli/env settings.

This version is somewhat improved in terms of robustness beyond the initial 
release.

Testing
-------

The following should result in a deployment with the Juju GUI and haproxy. Going to the 
exposed haproxy port will get you the admin interface to rethinkdb.

juju bootstrap
juju deploy --repository . local:trusty/rethinkdb-docker rdb
juju expose rdb
sleep 60
echo juju debug-hooks rdb/0
juju add-unit rdb

juju deploy cs:precise/juju-gui
juju expose juju-gui

juju deploy cs:precise/haproxy
juju add-relation haproxy rdb
juju expose haproxy