It needs to run as soon as the DataSource is available really otherwise
anything else that depends on the DataSource (like Security JDBC
initializers) might fail when it tries to use it.

One change from 1.1.1 is that if you have a schema.sql you had better
make sure your data.sql talks to the same tables. In 1.1.1 you could
sometimes get away with letting Hibernate initialize the tables for
your data.sql and *also* have a schema.sql. This was fragile and doomed
to fail eventually if the DataSourceInitializer somehow got
initialized earlier (e.g. through a @DependsOn), so in the spririt
of honesty being the best policy we explicitly disallow it now.

Fixes gh-1115