Various minor enhancements and bug fix

I needed to specify a custom table prefix so I made this an option. I also needed to add additional configs to wp-config.php. Rather than add a bunch of parameters, I made it so you can just include a template and it will get included in the wp-config.php.erb file itself. 

There was also a minor bug that I noticed where puppet every time it ran would change the grants. It seemed to be looking for the ALL permission when we had specified 'all'. Arguably this could be changed in the puppetlabs-mysql module, but this seems easier.