ISPN-2538 Endless loop in TreeMap.remove at shutdown of query-enabled

cache

* Changed map to be synchronized

https://issues.jboss.org/browse/ISPN-2538
It's just a Map implementation. Semantically this could use an HashMap, I generally like TreeMap when using string keys, but seeing that this should have been concurrent a ConcurrentHashMap might be a better choice.

So shutdown of caches is performed in parallel?