Fix for JCLOUDS-655

First time committing to jclouds, let me know if there are any style guidelines I missed with this change.
Both `getComplexMetadata()` and `getMetadata()` will need to be documented very well. Please explain why each one exists and that `metadata` will always be a subset of `complexMetadata`. Explain what kind of `Object`s can be returned in the `Map<String, Object>`