Fix for default log category breaks YUI Test

From IRC: 

"Example: I've added a Tree test that fails. I run the unit tests (in the browser, grover, or yet), and they report 1 failure. Nowhere in grover or yeti does anything actually tell me *which* test failed. In the browser, the test console no longer highlights failed tests in the log or allows me to filter the log to show only failures, so I have to scroll through every single passing test to find the one that failed.
s/yet/yeti/" 

"...As far as I can tell, log messages from tests just aren't being logged to the correct log levels anymore. Every single message gets logged as "info", and nothing gets logged as "pass" or "fail" or "status".
Used to be only the final summary was logged as "info", only passing tests were logged as "pass", and failing tests were logged as "fail"."

"Looks like this commit is what broke test logging: https://github.com/yui/yui3/commit/dacc8fe4c3dec46622db8790583c733b206fec35
Log categories are no longer allowed to be arbitrary (which is a feature tests depended on), and must now exist in the hard-coded set of levels in yui-log.js."