Run behave as subprocess command and return process/shell instance
    with results (collected output, returncode).

def behave(cmdline, cwd=".", **kwargs):
    """
    Run behave as subprocess command and return process/shell instance
    with results (collected output, returncode).
    """
    assert isinstance(cmdline, six.string_types)
    return run("behave " + cmdline, cwd=cwd, **kwargs)