Specify velocities for trajectory forwarding test

[fmauch]

Otherwise the trajectory points will never be sent.

[urrsk]

Why does it never get sent?
Due to our new check on splines?

[fmauch]

Why does it never get sent? Due to our new check on splines?

Basically because of the logic in HardwareInterface::startJointInterpolation()

    if (!use_spline_interpolation_)
    {
      // write point for movej command
    }
    else  // Use spline interpolation
    {
      if (point.velocities.size() == 6 && point.accelerations.size() == 6)
      {
        // write quintic spline segment
      }
      else if (point.velocities.size() == 6)
      {
        // write cubic spline segment
      }
      else
      {
        // nothing being sent
        ROS_ERROR_THROTTLE(1, "Spline interpolation using positions only is not supported.");
      }
  }

In the test we use a position-only trajectory so we end up in the last case, where no trajectory point is being sent, as we default to spline-interpolated execution. Since in the past we used the movej interface by default, the test actually was working correctly and got missed when switching to spline interpolation by default, as it was falsely succeeding. UniversalRobots/Universal_Robots_Client_Library#184 implements actually failing if no trajectory point was received, so the trajectory execution in the test fails.

Things could tremendously improved as explained in #722 but I wanted to keep this one small to get it implemented, reviewed and merged quickly, so this isn't blocking UniversalRobots/Universal_Robots_Client_Library#184 anymore.

[urrsk]

That makes sense.