Evergreen is going to implement a "degraded" mode if it cannot respond to test history queries due to load. In that mode, queries to the test history will return HTTP 503 (See https://jira.mongodb.org/browse/EVG-5633). We should detect this condition when attempting to split up test suites and divide up the suites randomly (we may want to define an expansion on the project of how much to divide up in this situation, that would allow us to change the value without needing to commit new code).