The basedir was mainly set correctly, but sometimes not used in some of
the tests. Let's move the `os.chdir` to `setUp` phase where it makes
sense and add new ones where they were not present.

Related to basedir the test_mux was using hardcoded path based on the
method used to execute the test, let's change it to `__file__` which
gives better results.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>