Prune leading 0 from filemodes

Summary:
That allows to be coherent between the different states,
where sometimes 0ugw is used, sometimes ugw.

As a dubious benefit, we can also load SLS as YAML
directly through PyYAML and avoid the octal to integer
convert. Salt correctly parses those values.

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2633