Apparently somewhere in the code we rely on the wagon filename to remain in the format that Wagon creates it.
Steps to reproduce:
1. Download openstack plugin wagon and yaml.
2. Change the wagon name to test.wgn.
3. Attempt to upload plugin to manager (cfy plugins upload test.wgn -y plugin.yaml).
This will break.
We shouldn't be relying on the filename for anything. There is a metadata file inside the wagon - we should be using it instead.