enable spawner to wait indefinitely if requested (#428)
enable spawner to wait indefinitely if requested (#428)

`rospy.wait_for_service` does not allow for `0` to wait indefinitely.
Instead, `None` has to be passed explicitly.

By personal request of three maintainers extended to include documentation
and the alternative argument --no-timeout.
ros-controls/ros_control,ros-controls/ros_control