Update mysqltuner.pp

Enable present/absence.. in those cases when you only want mysqltuner installed for debugging
Merge pull request #273 from davidcollom/patch-1

Update mysqltuner.pp
Remove mysql::globals.

This turned out to be a fairly bad idea.  It begun as a way to try
and mirror what happens in the postgresql module for consistency
but instead made things complex.

I've changed it to have the override_options in mysql::server which
leads much more naturally out of the design and shape of MySQL.
Merge pull request #278 from apenney/fix-globals

Remove mysql::globals.