Add workaround for pytest 3.3.0 bug
    
    pytest is setting an env var PYTEST_CURRENT_TEST to the test name + test
    parameters. If parameters happen to contain NULL bytes, the putenv()
    call fails with "ValueError: embedded null byte". The workaround uses
    repr() of test parameters as parameter id.
    
    See https://github.com/pytest-dev/pytest/issues/2957
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>