select/cray: set default TopologyPlugin

The select/cray plugin discovers the topology as part of its initialisation and
generates a node ranking. No further topology information is required by the
plugin, hence this patch sets the default TopologyPlugin to topology/none.

src/common/read_config.h

@@ -138,7 +138,7 @@ extern char *default_plugstack;
 #define DEFAULT_SWITCH_TYPE         "switch/none"
 #define DEFAULT_TASK_PLUGIN         "task/none"
 #define DEFAULT_TMP_FS              "/tmp"
-#ifdef HAVE_3D
+#if defined HAVE_3D && !defined HAVE_CRAY
 #  define DEFAULT_TOPOLOGY_PLUGIN     "topology/3d_torus"
 #else
 #  define DEFAULT_TOPOLOGY_PLUGIN     "topology/none"