so S3ArtifactStoreGetter can call a username-based hasPermission method.
FiatPermissionEvaluator has this method, but using FiatPermissionEvaluator in kork would
create a circular dependency.

The plan is:

- publish a kork jar with UserPermissionEvaluator,
- consume it in fiat and change FiatPermissionEvaluator to implement UserPermissionEvaluator instead of PermissionEvaluator
- publish a fiat jar and consume it everywhere
- change S3ArtifactStoreGetter to use UserPermissionEvaluator to fix the bug that spinnaker#1178 demonstrates
- publish yet another kork jar and consume it everywhere to fix use of fetchReference in Evaluate Variables stages