There are 2 changes in this PR:
1) Add a new environment variable called `DISCOURSE_SKIP_CSS_WATCHER` to disable our stylesheet watcher, and make the `qunit:test` rake task set this variable on the Unicorn/Rails server it spins up to disable our stylesheet watcher when running the tests because it doesn't really need it.
2) Print more Chrome logs (such as network/security errors) to the console.
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