Never run data.sql scripts if spring.datasource.initialize is false

Previously, the data scripts were always run in response to the
publication of a DataSourceInitializedEvent, irrespective of
spring.datasource.initialize. While the event won't be published by
DataSourceInitializer if spring.datasource.initialize is false, it
will be published if spring.jpa.hibernate.hbm2ddl.auto has been set.

This commit updates DataSourceInitializer's handling of
DataSourceInitializedEvent to only run the data scripts if
spring.datasource.initialize is true.

Fixes #1336