driver: log (more) appropriate msgs when topic_list is not found

In most cases this is not necessarily a problem, as single-group systems fi are not expected to not have that parameter.

So log an INFO message and continue trying to read the single-group config from the 'controller_joint_names' parameter (if that can't be found, we have a good reason to complain / refuse to continue).

Keep the WARN for one particular case: users starting the multi-group version of the JTA, but then *not* correctly setting the 'topic_list' parameter should be warned.

Thanks to @cjue who proposed the initial fix (in #483), which I've slightly expanded upon here.

motoman_driver/src/industrial_robot_client/joint_trajectory_action.cpp

@@ -60,7 +60,15 @@ JointTrajectoryAction::JointTrajectoryAction() :
   pn.param("constraints/goal_threshold", goal_threshold_, DEFAULT_GOAL_THRESHOLD_);
 
   std::map<int, RobotGroup> robot_groups;
-  getJointGroups("topic_list", robot_groups);
+  if (!getJointGroups("topic_list", robot_groups))
+  {
+    // this is a WARN as this class is the multi-group version of the regular JTA,
+    // and we're actually expecting to find the 'topic_list' parameter, as using
+    // this multi-group version with a single-group system is unnecessary and also
+    // doesn't make much sense.
+    // It probably also won't work.
+    ROS_WARN("Expecting/assuming single motion-group controller configuration");
+  }
 
   for (size_t i = 0; i < robot_groups.size(); i++)
   {

motoman_driver/src/industrial_robot_client/joint_trajectory_interface.cpp

@@ -92,6 +92,7 @@ bool JointTrajectoryInterface::init(SmplMsgConnection* connection)
   }
   else
   {
+    ROS_INFO("Expecting/assuming single motion-group controller configuration");
     this->version_0_ = true;
     std::vector<std::string> joint_names;
     if (!getJointNames("controller_joint_names", "robot_description", joint_names))

motoman_driver/src/industrial_robot_client/robot_state_interface.cpp

@@ -92,6 +92,7 @@ bool RobotStateInterface::init(SmplMsgConnection* connection)
   }
   else
   {
+    ROS_INFO("Expecting/assuming single motion-group controller configuration");
     this->version_0_ = true;
     std::vector<std::string> joint_names;
     if (!getJointNames("controller_joint_names", "robot_description", joint_names))