[usecase-webapi][XWALK-2353] Update the url path for mediarenderer

- Update the url path to absolute path
- Failure analysis: The prefetchURI method and mute method cannot work

Impacted tests(approved): new 0, update 1, delete 0
Unit test platform: [Tizen IVI]
Unit test result summary: pass 0, fail 1, block 0
Merge pull request #914 from yunxliu/yunxliu/misc/mediarenderer

[usecase-webapi][XWALK-2353] Update the url path for mediarenderer