Add basic tests for global router rate limits.

This changes the default burst, since I think these tests indicate burst
wasn't working as I had expected.

This also changes around how rate limits are handled in testing, which I
think is a bit better. Now the global rate limits can be completely
turned off during tests (instead of us just setting the rate limits
super high in the test environment). This allows us to still test the
default rate limits, while also ensuring we don't accidentally run into
the rate limits in our other tests.