Support Amazon RDS (w/ MySQL and Aurora) with MySQL Connector

Amazon RDS provides a relational database service using several different DBMS engines, including MySQL and Amazon Aurora. Amazon claims "The Amazon Aurora database engine is fully compatible with MySQL 5.6 using the InnoDB storage engine." However, neither RDS' MySQL or Aurora engines support the FLUSH TABLES WITH READ LOCK statement, and so the current MySQL connector always fails when it gets to this point.

The MySQL connector should not try to acquire the lock when it is connecting to one of these engines. (Hopefully we can discover we're using one of Amazon's engines by looking at the system variables.) This would potentially impact the consistency of the snapshot – the connector uses these locks because MySQL transactions do not prevent DDL changes, and the lock is the only way to prevent DDL changes while the connector is copying the table schemas. (See DBZ-31 for background on the existing snapshot algorithm.)