[webapi][xwalk-3179] Decrease timeout of AlarmRelative_getRemainingSeconds_return_null

Impacted tests(approved): new 0, update 1, delete 0
Unit test platform: [IVI]
Unit test result summary: pass 1, fail 0, block 0
Merge pull request #1506 from haoxli/webapi/xwalk-3179

[webapi][xwalk-3179] Decrease timeout of AlarmRelative_getRemainingSeconds_return_null