Better checking of optimisation in the Relax_disp system tests.
This affects the Relax_disp.test_hansen_cpmg_data_LM63 and Relax_disp.test_hansen_cpmg_data_CR72
system tests. Instead of using the auto-analysis, these tests now set the initial parameters close
to the minimum, skip the grid search, and perform a low precision optimisation to reach the minimum.
This is important because the low quality grid search and optimisation can not always find the real
minimum.
