Allow to create MySQL database
How can we create a database for a new phpBB instance?
The wrapper script runs on the Docker Engine host
and can interact with the SQLite database there,
but not with the MySQL server, as it's in a container.
The wrapper script will so run a container with this
mainteannce script to create the database.
The wrapper part is implemented at D1524.
Test Plan: saas-phpbb sites:createdb foo
Reviewed By: dereckson
Differential Revision: https://devcentral.nasqueron.org/D1573