Bug - 1008 Define checked exceptions

- introduced ConnectionException

Change-Id: I9b5c8594ecc1a4e3134a1643f961970f88a76eda
Signed-off-by: Martin Bobak <mbobak@cisco.com>
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>