Make use of Spring 4.3 background Hibernate initialization

[philwebb]

See https://jira.spring.io/browse/SPR-13732 - We need #5082 first

[snicoll]

We need to have our generally purpose AsyncTaskExecutor first (see #5082).

[snicoll]

If the user has defined an AsyncTaskExecutor that is primary, maybe we should automatically enable that feature. Thoughts?

[vpavic]

Hey @snicoll, I did some work on addressing this and was about to create a PR when I saw you've recently assigned the issue to yourself.

My changes are available here, let me know if I should go ahead with the PR. Thanks.