Fix disabled tests on FreeBSD Commit "Use generic os name in tests" (1f70f876d670704bd0422fe1e27d12177b189527) accidentally disabled testing on FreeBSD by adding double negation to condition that enables code for operating systems with fusermount(1). However fusermount(1) is not available on FreeBSD and therefore all regression tests were skipped. Fixes #93

Fix building on FreeBSD Cirrus CI on FreeBSD failed because "No packages available to install matching 'py37-pip' have been found in the repositories"i [1]. Package 'py37-pip' has been replaced with 'py38-pip', see [2]. 1. https://cirrus-ci.com/task/6375178809638912 2. https://www.freshports.org/devel/py-pip/