mandos-ctl: Refactor

* mandos-ctl (domain): Rename to "dbus_busname_domain".  Delete after
                       use.
  (busname): Rename to "dbus_busname".  All users changed.
  (server_path): Rename to "server_dbus_path".  All users changed.
  (server_interface): Rename to "server_dbus_interface".  All users
                      changed.
  (client_interface): Rename to "client_dbus_interface".  All users
                      changed.