[wrt]modify open_app to app_launch

[Detailed commit message (if have)]
Impacted TCs num(approved):New 0,Update 18,Delete 0
UT result: Pass 10, Fail 5, Block 3
BUGID:https://crosswalk-project.org/jira/browse/XWALK-2773
Merge pull request #1248 from linshen/shenlin/rename_open_app1

[wrt]modify open_app to app_launch