refactor to put a knob on all parameters

This  re-scopes all the variables in the params class to be mysql:: scoped parameters, which default to the values in params.pp. The stock behavior should not change, but one can now (with puppet3 or with a profile class) alter the value of variables which previously would require manual changes to module-owned files. 

The intention here is that people will be able to keep up to date with the forge module with greater ease as they will not need to make changes to the module to feed it customizations.