Remove Mongo.defineDbAuth function that takes a MongoClient as an argument and updated deprecation message for the other defineDbAuth functions.

When the new code for using MongoClient was added the functions that take a Mongo instance as argument were deprecated, including defineDbAuth. However, a subsequent update in the mongo-java-driver also deprecated DB.authenticate. Replaced by passing credentials in via MongoClient. So, I removed the new defineDbAuth function.
Replace MongoMeta.ensureIndex with createIndex.
Fixes #1573 - Failing Mongo Specs due to error message changes.
Merge pull request #1581 from lift/tcn_issue_1579

Deal with deprecations in mongo-java-driver v2.12