add worlddump tool to devstack

when we exit poorly, start building a tool for doing a capture
as to why. This tool is expected to be consumed directly from
grenade as well.

Change-Id: Ia1bc1c2e259587035ca7252baceec25fa464cb82
diff --git a/stack.sh b/stack.sh
index d2f18d4..5e2daf6 100755
--- a/stack.sh
+++ b/stack.sh
@@ -622,6 +622,11 @@
     # Kill the last spinner process
     kill_spinner
 
+    if [[ $r -ne 0 ]]; then
+        echo "Error on exit"
+        ./tools/worlddump.py -d $LOGDIR
+    fi
+
     exit $r
 }