ISPN-4301 Handle storeMetadata=false in JpaStore.process and JpaStore.purge methods

https://issues.jboss.org/browse/ISPN-4301
Having the tests disabled can be a bit confusing since we normally use them to point at unstable tests or known failures. Overriding the tests and leaving them with an empty implementation and a simple note on why this particular test is not relevant would be enough IMO.