Use established OpenStack API conventions in openstack-swift

This PR addresses the API changes as described in: https://issues.apache.org/jira/browse/JCLOUDS-545  

Accessing the `SwiftObject` metadata (with no body) is somewhat awkward with the current `head` request:

`SwiftObject head(@PathParam("objectName") String objectName);`

That said, I added a new method which describes the intent of the behavior:
`SwiftObject getWithoutBody(@PathParam("objectName") String objectName);`

`SwiftObject get()` returns the SwiftObject *with* content, so what is a more logical method name from a user's perspective?

Feedback is required before merging this PR!