Install rsyslog from its project package archive
Rsyslog can process supervisor and its own config
Log to data volume
Modularize init script

Now init scripts for individual configurations reside inside /app/init.d. This
way they can be passed through several stages of FROM directives. I.e. scripts
from lower layers (e.g. this base image) still are executed in containers
building upon those layers (provided supervisord is started!).
Log supervisord to container stdout

The supervisor logs are not guaranteed to be captured by rsyslog if rsyslogd is
(for whatever reason) not able to start properly. This makes capturing the
supervisord logs from outside the supervisord process necessary. I think the
container stdout is a proper channel for this, as some container metrics should
be captured from the outside anyway.
Add header including version to Dockerfile
Rename to mbrgm/service

In fact, this image is a base image for deployed services, and not to be used
as a generic base image.