Major Description
https://issues.apache.org/jira/browse/NEMO-55
simply ignores RPC failures to let the master live when executors fail, under the assumption that executor failures will be reported via the FailedEvaluator event. This probably is okay for handling common cases.
However in principle RPC failures should not be ignored. Either our interfaces in the edu.snu.nemo.runtime.common.message package should expose exceptions to the callers and all of local/ncs/grpc implementations comply with it, or we may remove the wrapping interfaces and expose one of ncs/grpc and its exception handling interfaces as-is.