Video: Fix speed menu when YouTube is unavailable.

This PR provides fix for [BLD-457](https://edx-wiki.atlassian.net/browse/BLD-457).

There is 2 cases that should be checked:
* Video player with Youtube link and without html5 sources and slow connection. Message in console: `Continue loading YouTube video`.
* Video player with Youtube link and with html5 sources and slow connection. Message in console: `Change player mode to HTML5`.

@valera-rozuvan please review.