Add "isPersistent" configuration option and adjust the test cases correspondingly

[mbroecheler]

That should help with the infinispan and hazelcast adapter and make the tests less "custom". In other words, the standard tests should be refactored to check this flag and the Infinispan/hazelcast/inmemory implementations don't need to be customized.

[dalaro]

Is this moot with ISPN and Hazelcast moved to titan-experimental?

Same question as Dan above. If the support was provisional and now gone, should this be closed ?