html: support #script-(on|off) directives for tests
html: support #script-(on|off) directives for tests

Those directives are now supported by html5lib-tests.
See: https://github.com/html5lib/html5lib-tests/blob/e52ff68cc7113a6ef3687747fa82691079bf9cc5/tree-construction/README.md

Also, this fixes missing opts on parsing for identical check

Change-Id: I92f2398ebda0477fd7f6bb438c54f3948063c08d
Reviewed-on: https://go-review.googlesource.com/c/net/+/206118
Run-TryBot: Kunpei Sakai <16e6eef4865510c955b62d2536a11db5146a1308@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Nigel Tao <58ae08b3356928ff9c67562b4719487d54fe8348@golang.org>

golang/net