Continuing on from ARTEMIS-4406, the calls to AbstractJournalStorageManager storeKeyValuePair + deleteKeyValuePair used by LocalCache as part of the connection-router implementation are themselves also not entirely thread safe.

A ConcurrentHashMap is used for the initial structure, however a regular HashMap sub-map is then stored within the concurrent outer map, which can then also be accessed concurrently, meaning the methods aren't currently thread safe; it also needs to be a ConcurrentHashMap.