[wrt][XWALK-890] update test.py to work on crosswalk-8.36.164

1.update check log to check db
2.add null value to seed file
3.add app launch to nagative seed file
4.add start/end time
5.update DB path
Merge pull request #398 from linshen/update-xwalk-890

[wrt][XWALK-890] update test.py to work on crosswalk-8.36.164