tests: fix vcs Hg helper functions get_user_name and get_user_email to actually use provided config_file

Running just test_get_user_name and test_get_user_email would fail when run as:
py.test kallithea/tests/vcs/test_repository.py -k test_get_user

The config file was not used at all, and the tests would only pass when
test_get_config_value had been run first and as an unfortunate side-effect had
read the same file.