Environment_classes endpoint will not cache data if given accurate etag

As part of a refactor in SERVER-2471 a bug was introduced where if the etag cache has been evicted but the requester submits a still valid etag the server will compute the class info for an environment (because the cache was empty) then check the computed etag value against requested etag and return a 304, but not cache the newly computed etag.

This means if there's a deploy that evicts an environment but doesn't change the class info for that environment, the cache will not be updated (despite returning 304) until a deploy where the environment changes its class content.

A work around for this exists, users may submit a request to the environment_classes endpoint without the etag. This will trigger the correct caching behavior. However, the console (the consumer of the environment_classes endpoint in PE) will always submit an etag for an environment if it has one.