fix issue 684 by allowing convenient running of custom init SQL statemen...

...ts during connection acquisition. Just added a new version of setDataSource which passes the initialization statements to DriverDataSource which already contains the functionality to run custom init statements.

Without the code in this pull request the functionality can be accessed by creating a DriverDataSource instance with the extra parameters and passing this instance to Flyway. I have used this method to test that the code in DriverDataSource works, but this was not an exhaustive test.