Misc changes and fixes

* Enforcing consistent use of terms like namespace and identifier
* Allowing the mongodb collection name to be specified in config
* Fixed flag validation in initFlag()
* Removed dead code in ragflagPerformSave
* Only upsert when flags are enabled, $unset flags instead of setting them to false
* Fixed the default connection uri for the tests (previously attempted to connect to "undefined/testRagFlag")
* Updated tests to deal with a) the naming changes for identifier & namespace and b) $unset instead of false