test: tidy up UtilLinux_test

this should eliminate test failures throw std::cout (for example if some xdg aren't installed)
Merge pull request #416 from karolherbst/travis

test: tidy up UtilLinux_test

we should clean up test anyway. Print something to std::out doesn't make sense.

Instead we should check fixed values against function results. After the 0.8 release we should create a lot of tests to stabilize desurium.