OperationFailure should be raised for legacy "wnote" write concern error

RUBY-732
jnote should raise Mongo::Operation

RUBY-732
wnote should raise Mongo::OperationFailure

RUBY-732
Test various bulk API commands and error-handling
Add documentation for bulk API find()
Stress tests for the bulk API
Refactor shared auth test framework to avoid namespace clash
Auth tests for the bulk API