BUG-956 deadlock by rpc invocation - phase2

- tuning Future chaining
- introduced ListeningExecutorService
- dereference used
- clean up after bulkTransactionCache removal
- add/update meter and group refactored in order to follow future responses and run in pool

Change-Id: I5c9367512c3ab6f1799f30dad1344667fde63991
Signed-off-by: Michal Rehak <mirehak@cisco.com>