Regression test differences obstructed by excessive logging

[jonmaddock]

Vast quantities of debug logs make it hard to see differences/failures in regression tests. I think this is pytest's default behaviour of including logs at all levels when an exception is raised. I believe this could be altered to still ignore DEBUG logs on a test failure, if this is a good idea.

...
DEBUG    process.io.mfile:mfile.py:63 Initialising variable 'vburn': Loop_voltage_during_burn_(V)
DEBUG    process.io.mfile:mfile.py:88 Scan 1 for variable 'vburn' == 0.038197311948930765
DEBUG    process.io.mfile:mfile.py:63 Initialising variable 'rplas': Plasma_resistance_(ohm)
DEBUG    process.io.mfile:mfile.py:88 Scan 1 for variable 'rplas' == 4.122773179768535e-09
...