[webapi][XWALK-2218] Updating workers TCs so that error info can be prin...

...t

- SharedWorker object defined in tests{}, so that if any undefined info can be print

Impacted TCs num(approved): New 0, Update 3, Delete 0
Unit test Platform: Tizen IVI
Tizen test result summary: Pass 3, Fail 0, Blocked 0