Add more unittests, smaller fixes to pytest configuration and useful scripts

Jan Hendrik Ebbing requested to merge jebbing/ILCDIRAC:more_unittests into Rel-v26r0

Current coverage 53% overall. Calculate coverage script now shows the exit status of each test suite at the bottom. The symlink caused all unit tests to be executed twice, this has been fixed. Added new utility functions for testing if a mock has been called appropriately & started refactoring to use it. Fixed assertContentEqualsList utility function (natural name, useful failure message, bugfix)

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