Return the config as text from a config tree.

def _print_config_text(tree, indentation=0):
    '''
    Return the config as text from a config tree.
    '''
    config = ''
    for key, value in six.iteritems(tree):
        config += '{indent}{line}\n'.format(indent=' '*indentation, line=key)
        if value:
            config += _print_config_text(value, indentation=indentation+1)
    return config