255 -> 1.0 for color::rgba + remove dead code lint

In build_display_list_abs (block.rs) and handle_reflow (layout_task.rs)
255 is incorrectly used instead of 1.0 for color::rgba (255 is correct
with color::rgb but *not* color::rgba).

In cors.rs remove the dead code warning for fn clear.
The function shouldn't be removed since it'll be used in the future
(fn clear is an implementation of http://fetch.spec.whatwg.org/#concept-cache-clear).
Merge pull request #2941 from bjwbell/change-255-to-1-for-rgba

255 -> 1.0 for color::rgba + remove dead code lint
Disable Range tests.
Update expectations.
Update run.sh and run.py for changes to wptrunner.
Make wpt use mach-style logging by default.
Don't ignore errors in wpt/run.sh.
Make wpt run as part of make check.
Run wpt on Travis.
Remove the expected timeout for EventTarget-dispatchEvent.html.

The test only times out in debug builds, and our continuous integration runs
non-debug builds.
Expect an unexpected timeout in responsetext-decoding.htm.
Cleanup run.py and config.ini.
Remove assignments to args.metadata_root and args.tests_root in run.py.
Pin wptrunner to version 1.0.