Genralising docker-gen for database use-case

[phil-lello-gb]

I am considering forking docker-gen (which means learning go) to support the following flow:

• docker-gen listens for enviornment variables DB_HOST, DB_USER, DB_PASSWORD, DB_NAMESPACE (or less offensive generalisation)
• when a container starts the docker-gen host spits out and applies SQL of a "IF NOT EXISTS CREATE DATABASE xxx; GRANT ALL ON xxx TO yyy' persuasion

From what I can tell, the missing element from the existing software is the list of variables - or perhaps the documentation reflects the initial purpose and this is already possible - making this a "Documentation Request" rather than "Feature Request"

In the considered use-case there may be issues relating to multiple services and host/network naming.

[phil-lello-gb]

I must stop coding when I'm too tired. Meanwhile, here's an "good enough for dev" implementation of automated DB creation against mariadb. Since it is an mysql variant, no doubt the syntax will need tweaking depending on day of week, ambient temparature, mother's maiden name, and so on.

#462