Make object actions pass positional arguments

Port Commit 5d9cb7dd354dc1a1eae9985521c0f4b2ea4d876e from Nova.

This changes the Object API to also pass positional arguments
to remotable methods. Previously, we required only keyword arguments
to these methods in order to mirror our current RPC behavior.
This is not really necessary and could be confusing.

Change-Id: Icd725a2df48883564c0ac131a9a8ef33817f30c5
Merge "Make object actions pass positional arguments"