Save Peer Status separately in the FileStore (#554)

Due to peer reconnects when restarting the Management service,
there are lots of SaveStore operations to update peer status.

Store.SavePeerStatus stores peer status separately and the
FileStore implementation stores it in memory.

management/server/management_proto_test.go

@@ -398,7 +398,7 @@ func startManagement(t *testing.T, port int, config *Config) (*grpc.Server, erro
 		return nil, err
 	}
 	s := grpc.NewServer(grpc.KeepaliveEnforcementPolicy(kaep), grpc.KeepaliveParams(kasp))
-	store, err := NewStore(config.Datadir)
+	store, err := NewFileStore(config.Datadir)
 	if err != nil {
 		return nil, err
 	}