Give the suite runner some more time in an intermittently failing test

300ms is not enough apparently, it fails sometimes when running in Overman
Make the third parameter to run_test.js JSON instead of a number

I want to pass more than just a test timeout; in particular, I want to pass the
slow threshold too. There are also other things that would be good to add, for
example interface parameters, so this seems like a good addition.
Add support for getting and setting slow thresholds in the BDD mocha interface

Support in the actual test runner and suite runner is coming soon
Add support to the suite runner for getting and setting slow thresholds

The value isn't used anywhere yet.