[html-tests] Unbreak and rename the autoplay vs. preload test (#687)

It was broken since loadstart is fired regardless of preload.
A later event must be used, e.g. playing.

Test both orders of setting the attributes.
Blink fails with one order but not the other.

View on GitHub: https://github.com/w3c/web-platform-tests/pull/687

Received on Sunday, 23 February 2014 10:06:40 UTC