Support moving from 2.6 MONGODB-CR to 2.8 MONGODB-CR/SCRAM and vice versa.
Support moving from 2.8 MONGODB-CR/SCRAM to 2.8 SCRAM only
Document SCRAM-SHA-1 upgrade/downgrade process
Resurrect or remove checkReplicaMemberVersions function for auth schema upgrade compatibility check
Implement the SCRAM-SHA-1 SASL Mechanism
All authentication fails when auth schema version 4 used with SCRAM as only mechanism