Bug - 1008 Define checked exceptions

- IllegalStateException thrown by MessageDispatchServiceImpl#getConnectionAdapter
  is replaced by ConnectionException
- all Future<RpcResult<T>> methods return RpcError wrapped in RpcResult if
  ConenctionException is thrown by MessageDispatchServiceImpl#getConnectionAdapter
  when method is called
- openfloplugin-api bundle added to integration tests

Change-Id: Ib930dfc2ab19e56eea43022b586979c6bc52d034
Signed-off-by: Martin Bobak <mbobak@cisco.com>