[COOK-3597] Implementation of initdb_locale attribute for EL (redhat/centos/etc) distros

https://tickets.opscode.com/browse/COOK-3597

Added code and one default/new attribute named "initdb_locale" that allows specifying the initdb locale desired by the user, independently from the current system locale.

initdb currently is ran with default parameters and uses the system locale. Sometimes you must have a system locale that is not what you want for your database, and this attribute addresses that scenario.

This is valid only for EL-family distros (RedHat/Centos/etc), and the distro's original init script supports passing a locale parameter to initdb. I am only making possible for this cookbook to use that same feature/parameter, which is essential in some situations.