Timestamps laserscan messages

[rostest]

The timestamps in the header of pointcloud messages (i.e. msg.header.stamp of ros::sensor_msgs::PointCloud2 messages) are lidar ticks converted to ros-time using a software pll. The timestamp in the header of laserscan messages (msg.header.stamp of ros::sensor_msgs::LaserScan messages) ist the ros-time when receive the telegram. The timestamp of the laserscan messages should be identical to the timestamp of pointcloud messages.

[rostest]

Release 2.6.3: Timestamp of pointcloud and laserscan messages identical and computed from lidar ticks by software-pll