RobotFramework 3.2.x版本特性变化

https://github.com/robotframework/robotframework/blob/master/doc/releasenotes/rf-3.2.rst#id151

1. 测试用例解析文件后缀名调整为缺省仅解析“.robot”文件。需要解析其它如，“.tsv”、“.txt”文件时，需要在执行参数加上“--extension robot:tsv:txt”参数。

robot --extension robot:tsv:txt 

Only *.robot files are parsed by default

2. 测试目录解析API由robot.api.TestDataDirectory调整为robot.running.TestSuiteBuilder。

# after RF 3.2.x
from robot.running import TestSuiteBuilder
root_tc_node = TestSuiteBuilder(included_extensions=('robot','tsv','txt')).build(rf_source)

# before RF 3.2.x
from robot.api import TestDataDirectory
root_tc_node = TestDataDirectory(source=rf_source).populate()

Parsing APIs have been rewritten