Fix distributed master shutdown

Summary:
Master shouldn't stop processing rpc calls immediately on shutdown. It
should wait for all workers to stop, and then destroy itself.

Reviewers: dgleich, mferencevic

Reviewed By: dgleich

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D1330

src/communication/rpc/client.hpp

@@ -46,7 +46,7 @@ class Client {
       return nullptr;
     }
 
-    if (VLOG_IS_ON(12)) {
+    if (VLOG_IS_ON(12) && response) {
       auto res_type = utils::Demangle(response->type_index().name());
       LOG(INFO) << "[RpcClient] received "
                 << (res_type ? res_type.value() : "");

src/database/graph_db.cpp

@@ -160,13 +160,6 @@ class Master : public PrivateBase {
     return index_rpc_clients_;
   }
 
-  ~Master() {
-    // The server is stopped explicitly here to disable RPC calls during the
-    // destruction of this object. This works because this destructor is called
-    // before the destructors of all objects.
-    server_.StopProcessingCalls();
-  }
-
   communication::rpc::Server server_{
       config_.master_endpoint, static_cast<size_t>(config_.rpc_num_workers)};
   tx::MasterEngine tx_engine_{server_, &wal_};

src/distributed/coordination_master.cpp

@@ -47,6 +47,9 @@ MasterCoordination::~MasterCoordination() {
     auto result = client.Call<StopWorkerRpc>();
     CHECK(result) << "StopWorkerRpc failed work worker: " << kv.first;
   }
+
+  // Make sure all StopWorkerRpc request/response are exchanged.
+  std::this_thread::sleep_for(2s);
 }
 
 Endpoint MasterCoordination::GetEndpoint(int worker_id) {