How to fix "Unable to instantiate JDBC driver" Flyway command line error?
Problem solved. For Oracle you have to put the jdbc driver jar in the drivers sub directory.
This is documented here.
In summary: Go to http://www.oracle.com/technetwork/database/features/jdbc/index-091264.html and choose the required Oracle JDBC driver version. Then download the "ojdbc6.jar" file and move it into the drivers folder beneath where Flyway is installed. The next time you run Flyway this should be picked up automatically.