The responsibility of setting up the test environment has been delegated to
the tests themselves by providing a base class. Therefore, every test that
needs this environment will have to be a subclass of BaseClass.

It is still being investigated if this could be more neatly implemented
with a decorator.

The first test proved to be useful because Network::getIfaces() didn't
check for virtual network interfaces. When changing its implementation to
fix this, an E127 syntax error was repoted by `make check-pylint`, so it
has been disabled.
setup_test_environment.sh: minor change for code clarity.
Since this tool is meant to be used with super-used privileges, there is no
need to use `sudo`.