[webapi] Avoid add testharness repeatedly

- In some tests, testharness.js has been added by unitcommon.js, add testharness.js repeatedly will create a timeout result, so update it following unitcommon.js

Impacted tests(approved): new 0, update 0, delete 0
Unit test platform: [IVI]
Unit test result summary: pass 188, fail 18, block 1
Merge pull request #1497 from haoxli/webapi/tizen-systeminfo-update

[webapi] Avoid add testharness repeatedly