At the time of writing WAS only supports JPA 2.0 which means that
Hibernate 4.2 is the latest version that can be used. SpringJtaPlatform
is Hibernate 4.3-specific as JtaPlatform’s package changed between
Hibernate 4.2 and 4.3. This means that SpringJtaPlatform can’t be used
on current versions of WAS. Futhermore, SpringJtaPlatform won’t work on
WAS even if we could use Hibernate 4.3 as WAS doesn’t make its
TransactionManager available to application code (it’s considered too
dangerous for general consumption) and SpringJtaPlatform
requires a TransactionManager.

This commit updates HibernateJpaAutoConfiguration to always treat WAS as
a special case and configure Hibernate with one of its WAS-specific
JtaPlatform implementations. 

Closes gh-2326