[wrt] update tcs for sampleapp/Crosswalk_SampleApp_WebRTC_Launch.html

Impacted TCs num(approved): New 0, update 3, deleted 0
Unit test platform: [tizen]
Unit test result summary: Pass 3   , Fail  0, Blocked  0
Merge pull request #241 from linshen/modify-webrtc-tcs

[wrt] Fix XWALK-1636/1645 to update  test step