JGroupsTransport instance is reused in tests

The TRANSPORT AttributeDefinition uses IdentityAttributeCopier, which means that when a test uses GlobalConfigurationBuilder.read() to make a clone of the global configuration it keeps using the same JGroupsTransport instance. Both cache managers sort of work, but usually not as intended.

We should detect when JGroupsTransport's dependencies are injected twice and throw an exception. We should also consider changing the TRANSPORT copier to SimpleInstanceAttributeCopier.