Fix get load tests

Based on https://github.com/sdesai/yui3/commit/ca6eff84d77b3fe80de4832b45c7e60091993195

Removes echoecho delays where they are not needed, and resolves the following issues:

1. The purge test which loads 30 scripts was occasionally hitting the 30s `test.wait()` timeout. Rather than bumping up the timeout, delays were removed from this test since it didn't add much value to what was being tested.
1. On browsers that don't fire an event when CSS fails to load, Get uses a default timeout of 3000ms. Our CI environment hits this limit often, so we now bump up the timeout for these browsers (e.g. IE9).