Fix a test failure on WiredTiger (db dropped after last collection is dropped).
Fix a test failure on WiredTiger (db dropped after last collection is dropped).

mongodb-labs/mongo-connector,agolo/mongo-connector,10gen-labs/mongo-connector,10gen-labs/mongo-connector,XDestination/mongo-connector,sailthru/mongo-connector,ShaneHarvey/mongo-connector,ShaneHarvey/mongo-connector,XDestination/mongo-connector,mongodb-labs/mongo-connector,sailthru/mongo-connector,agolo/mongo-connector