Functional tests use x-auth-token rather than x-storage-token

This change allows other auth systems to test against the functests but not
require them to support x-storage-token (which was deprecated before swift
was even open-sourced). All other places in the code where x-storage-token is
used is only to populate x-auth-token if x-auth-token doesn't already exist.

Change-Id: Ie903d0f7135fc643353b74a61c14becf7dfc4d9d