ref-arch, 3nodes: Force cloud class to step 1 of every profile

The cloud class is common to every node, it needs to happen at step1.
The way it was done before was functional, but could leave the classes
array in hiera file empty, thus resulting in a parsing error.
Merge pull request #9 from enovance/fix_nilClass_on_missing_classes

ref-arch, 3nodes: Force cloud class to step 1 of every profile