Fix flake in high playback rate test
Fix flake in high playback rate test

Something weird happens on some platforms (variously Chromecast, IE,
legacy Edge, and Safari) where the playhead can go past duration.  To
cope with this, don't fail on timeout.  If the video never got flagged
as "ended", check for the playhead to be near or past the end.

Also, wait for playback to begin before increasing the playback rate.
This improves test reliability on slow platforms like Chromecast.

Change-Id: If7d70de95b75e602853ec77ad1c285c118875db4

shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,tvoli/shaka-player