Resolve premature controller initialization (#213)

Squashed commits:

* Avoid updating ros_control controllers on pipeline timeout
* Revert "Avoid updating ros_control controllers on pipeline timeout"
* Do not update controller_manager until RTPackets have been received
* Mark handles as initialized after actually doing it rather than just before
* Improve readability

include/ur_modern_driver/ros/controller.h

@@ -19,6 +19,7 @@ private:
   ros::NodeHandle nh_;
   ros::Time lastUpdate_;
   controller_manager::ControllerManager controller_;
+  bool robot_state_received_;
 
   // state interfaces
   JointInterface joint_interface_;