Update acceptance tests to use real duration of YouTube video.

**Description**

The YouTube stub server should actually get real duration of YouTube video, and pass that on to the video player instance on front end. If YouTube stub sever doesn't do this, then when the Play button will be clicked in the video player, the video will begin playing, and the API will report a totally different duration than was previously determined form the metadata (YouTube stub server responds with metadata information for acceptance tests).

**Reviewers**

- @polesye 
- @auraz