[webapi] Change 2 cases from manual to auto for webgl

- These two case can be performed automatically, so change the execution type to auto.

Impacted TCs num(approved): New 0, Update 2, Delete 0
Unit test Platform: [Tizen-IVI]
Unit test result summary: Pass 2, Fail 0, Blocked 0
Merge pull request #1530 from JianfengXu/webgl/automation

[webapi] Change 2 cases from manual to auto for webgl