BGQ - update debug message to spell out what is going on better when

picking cnodes for a step.

src/plugins/select/bluegene/ba_bgq/block_allocator.c

@@ -1001,7 +1001,8 @@ try_again:
 				bit_not(ba_mp->cnode_bitmap);
 				info("ba_pick_sub_block_cnodes: "
 				     "using cnodes %s on mp %s "
-				     "leaving '%s' usable in this block (%s)",
+				     "leaving '%s' on this midplane "
+				     "usable in this block (%s)",
 				     jobinfo->ionode_str,
 				     ba_mp->coord_str, tmp_char,
 				     bg_record->bg_block_id);
@@ -1107,8 +1108,8 @@ extern int ba_clear_sub_block_cnodes(
 				ba_mp->cnode_bitmap, ba_mp_geo_system);
 			bit_not(ba_mp->cnode_bitmap);
 			info("ba_clear_sub_block_cnodes: "
-			     "cleared cnodes %s on mp %s, making '%s' usable "
-			     "in this block (%s)",
+			     "cleared cnodes %s on mp %s, making '%s' "
+			     "on this midplane usable in this block (%s)",
 			     tmp_char, ba_mp->coord_str, tmp_char2,
 			     bg_record->bg_block_id);
 			xfree(tmp_char);