launch_instance.sh: return error if nova-compute fails

If the nova-compute service is up but remains offline (XXX) in
nova-manage service list, the script gives up, returning 0 (success) as
the exit code.

This patch makes this case return 1 (error) instead which is consistent
with similar cases in the script.

Change-Id: Ia6945569255a7cd9796930edff21ffcfc333cc1d

labs/scripts/test/launch_instance.sh

@@ -127,9 +127,9 @@ function wait_for_nova_compute {
                 grep -q "start/running"; then
             if [ $cnt -eq 300 ]; then
                 # This should never happen.
-                echo "SUM ERROR nova-compute remains XXX while up."
+                echo "SUM ABORT nova-compute remains XXX while up."
                 echo "Aborting."
-                exit
+                exit 1
             fi
             echo -n .
         else