WL#7307: Fold mysql_install_db into the server binary

The database bootstrap process uses and odd (and extremely fragile) mix of a 
special server startup mode, an SQL script and some shell scripting glue.

This results in a very unportable, complex and non-flexible bootstrap procedure. 
Up to the point where we actually need to distribute an empty set of database 
files inside the installer for our primary OS (MS Windows) !

This worklog is about uniting the whole boostrap ritual sequence into a single 
server option : just specifying --bootstrap on the server command line will be 
enough to create a database directory if it's absent or empty. 
Or prevent the server from starting up if a database directory is already present.