Added factory method to construct MongoClient with a MongoClientURI
Added MongoClientAdapter constructor that takes a MongoClientURI
Added support for MongoURI/MongoClientURI constructors
Added support for constructing test MongoClient instances from a URI specified via system property
Working around bug where no read preference is set on a query
Replaced hard-coded db name with reference to constant
Added gradle support for passing in mongodb URI as a system property when running tests