Set env vars for supervisor in custom init script.

* Modify init.d script from Debian package.
* Remove old, crappy way of reading env vars in msm-redis-listener.py.
Rely on DATABASE_URL being set in backup script.

* Don't read /etc/environment directly in
  msm-manage-pre-shutdown-backup.py.
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.
Read /etc/environment in /etc/init.d/msm-update-instance-state.

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

* Going back to os.getenv()
Call different backup to S3 script in build-ami.py.

* Now using `msm-pre-shutdown-backup.sh`.
Make supervisor init script executable.