[#61573276] update settings.py configuration for (forced) update to 1.6.8

This fixes some issues with the way the mms-agent settings.py configuration was getting generated. Because of a lack of versioning on the MongoDB side (they only offer links to the latest version), there's no way simple way to lock down the version to avoid this.

https://www.pivotaltracker.com/story/show/61573276