Use rmw_qos_profile_sensor_data for joint_states source subscription

[smith-doug]

I'm using a robot that publishes joint_states with best_effort reliability. A best_effort subscriber can receive both best effort and reliable topics. See https://github.com/ros/robot_state_publisher/blob/72e73579d1ffe55e6d92c028d2b6bb311eed8770/src/robot_state_publisher.cpp#L146