[WFLY-547] track uncleanly unregistered slave hosts

https://issues.jboss.org/browse/WFLY-547

This requires some tricks with registering runtime resource, so if this and the model structure is OK, then i can add more information we expose.
1) We log this even if hostRegistration == null?
2) Logging this after DOMAIN_LOGGER.unregisteredRemoteSlaveHost(id) instead of before seems strange -- the log order should be cause then effect, not effect then cause.