[RSSotController] Better handle subsampling.

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  Formerly, when the computation of the graph was subsampled, computation was
  launched once in several iterations. As a result, the iteration when the
  computation was launched was usually exceeding Roscontrol time period and
  the scheduler would catch up at the next iteration since no computation was
  launched.

  With this commit, the computation of the control graph is launched in
  a separate thread in such a way that reatime constraints are satisfied.

[RCSotController] Save log in destructor

  instead of in method stopping.
  The ROS driver for UniversalRobot stops from time to time.
  When this happens, roscontrol process is stopped and restarted.
  Before this commit, saving the logs between stop and restart
  made the robot stop for a few seconds. This is undesirable.

Add RCSotController destructor

Move cleanup and log destruction to destructor in order to enable
stopping/starting with ROS controller manager

Fix formatting of error message.

Fix logs

fix CI

  The duration of each iteration was not logged in the line corresponding to
  the other data. The bug has been fixed and a test has been added to check
  the good functioning of the circular buffer.

to fix build on 20.04

fix submodule url