Rename `os project usage list` to `os usage list`
Rename `os project usage list` to `os usage list`

There really isn't anything project specific about the command,
it should really just be `os usage list`. For at least one
development cycle we should keep the old command.

Change-Id: I4d1df801576c259b527e87369f3121b94393cfa8

BjoernT/python-openstackclient,dtroyer/python-openstackclient,BjoernT/python-openstackclient,dtroyer/python-openstackclient,redhat-openstack/python-openstackclient,redhat-openstack/python-openstackclient,openstack/python-openstackclient,openstack/python-openstackclient