SITL Launcher: gzserver must be running when gzclient connects

Tools/sitl_run.sh

@@ -104,6 +104,9 @@ then
 		if [[ -n "$HEADLESS" ]]; then
 			echo "not running gazebo gui"
 		else
+			# gzserver needs to be running to avoid a race. Since the launch
+			# is putting it into the background we need to avoid it by backing off
+			sleep 3
 			gzclient --verbose &
 			GUI_PID=`echo $!`
 		fi