Add unittests for CombinedSoftwareInstallation, TARSoft
Also minor refactoring of tests that use File Operations. (Use utility method to check for correct IO)
GitLab jobs artifacts no longer stored forever as of Monday, November 4th 08:30h. Further information under https://cern.ch/otg0152576
Also minor refactoring of tests that use File Operations. (Use utility method to check for correct IO)