Fixes #3734: Rename SuSE to SUSE and keep SuSE* classes for backwards compatibility

This is a fix for Redmine #3734 (https://cfengine.com/dev/issues/3734).

I came across this bug recently and jumped on it because I am always confused too about the capitalization of the SuSE* classes, and usually get it wrong. Please consider this my contribution to making any SuSE-based CFEngine users happier.