Use NullPool to ensure DB connections close.
Install pip packages from requirements.txt.
Add backup scripts to run before shutdown.

* msm-manage-pre-shutdown-backup.sh checks to make sure
  instance state is 'running' before kicking off actual
  backup. Also, updates state in DB and memcache before
  and after backup.
* msm-pre-shutdown-backup.sh stops minecraft server, then
  performs backup to S3.
Run cronjobs as 'minecraft' user.

* Running 'msm-track-active-players' cronjob as root resulted in
  'server.log.offset' file being owned by root. Now, it will be
  owned by 'minecraft', allowing 'minecraft' user to run backups.
Don't need 'sudo' to call msm-pre-shutdown-backup.sh.
Change state names in msm-manage-pre-shutdown-backup.py.
Remove backup functions from init.d shutdown script.

* Syncing working files and backing up archives now happens
  before shutdown process is initiated.
Add msm-redis-listener.py.

* Listener will run continuously and wait redis pubsub messages
  on the 'command' channel. When it receives the 'backup' command
  from Minecloud webapp, it runs the msm-manage-pre-shutdown-backup.py
  script.
Configure supervisor to run 'msm-redis-listener.py'.

* Use Ubuntu package of supervisor, rather than installing with pip.
Add custom init script for supervisor.

* Modified script in Debian package.
Install custom init script for supervisor.
Add get_redis_url() to msm-redis-listener.py.

* When supervisor starts from init.d, the /etc/environment
  variables are not in it's environment. So, I'm manually
  reading the REDISTOGO_URL env var in msm-redis-listener.py.

`msm-redis-listener.py` now works, which fixes #6.
Add msm-update-download-url.py.

* Minecraft has new download URL for each new version. MSM
  doesn't handle this right now, so this script is a temporary
  fix until it does.

Fixes issue #5.
Update AMI in build-ami.py.
Switch to my fork of minecraft-server-manager.
Remove commented-out command.
Exit early if DATABASE_URL env var isn't set.
Delete get_redis_url() function.

* REDISTOGO_URL is one of the env vars from /etc/environment
  that is now exported in the supervisor init.d script. That puts
  it in this script's environment, so it no longer needa its own
  separate function to pull env var from /etc/environment.
Read /etc/environment in /etc/init.d/msm-s3-sync.

* Export vars in current environment. Don't call script
  using /usr/bin/env.
Read /etc/environment in /etc/init.d/msm-update-auth-lists.

* Export vars in current environment. Don't call script
  using /usr/bin/env.