glance-control need not locate a server's config file (lp#919520)
    
    Before converting to cfg, glance-control would use find_config_file() to
    locate the servers config file if the user did not explicitly specify
    it.
    
    With the change over to cfg, we screwed that code up. However, we should
    instead just allow the server to locate its own config file rather than
    trying to guess what it will use.
    
    Change-Id: I422839ae4c684ff2de3a0a96dd54c6b74ce6df97