Automatically update tolerances in testsuite

[jonasjucker]

Currently the tolerances for each parameter have to be edited by hand.
This is cumbersome and a waste of time.
Furthermore it makes it hard to reset the thresholds after a new ref has been uploaded.

Implement a tuning mechanism in https://github.com/C2SM/extpar/blob/master/test/testsuite/src/checkers/tolerance_check_cdo.py to achive that.

For cosmo this tuning option has been in place, I think here: https://github.com/C2SM/extpar/blob/master/test/testsuite/src/checkers/output_tolerance_check.py