[wrt][XWALK-1886] fix-xwalk-1886

Change assert_true() to async_test()
Impacted TCs num(approved): New 0, update 2, deleted  0
Unit test platform: [tizen]
Unit test result summary: Pass 2 , Fail  0, Blocked 0
Merge pull request #309 from linshen/fix-xwalk-1886

[wrt][XWALK-1886] fix-XWALK-1886 update tct-rt01-wrt-tests