Fix flaky acceptance test.
Merge pull request #3149 from edx/alex/fix_flaky_test

Fix flaky acceptance test.
HD control is disabled initially. It eventually gets enabled on first play of video, when player.getAvailableQualityLevels returns on non-empty array. [BLD-937]
Addressed comments.
Hide HD button on initialization instead of disabling. Show it if HD available instead of enabling.
Addressed comments. Fixed failing tests.
Fixed further tests.
Addressed latest comments.
Added getAvailableQualityLevels to HTML5 player.
Addressed Valera's comment
Renamed onFetchAvailableQualities to fetchAvailableQualities and moved it to 05_video_quality_control.js
Replaced play trigger by subscription. Added JSDoc comments.