lint: add errchecks (#5316)

## Description

Work towards enabling errcheck

ref #5059

abci/client/grpc_client.go

@@ -99,7 +99,9 @@ func (cli *grpcClient) StopForError(err error) {
 	cli.mtx.Unlock()
 
 	cli.Logger.Error(fmt.Sprintf("Stopping abci.grpcClient for error: %v", err.Error()))
-	cli.Stop()
+	if err := cli.Stop(); err != nil {
+		cli.Logger.Error("Error stopping abci.grpcClient", "err", err)
+	}
 }
 
 func (cli *grpcClient) Error() error {

abci/client/socket_client.go

@@ -413,7 +413,9 @@ func (cli *socketClient) LoadSnapshotChunkSync(
 func (cli *socketClient) ApplySnapshotChunkSync(
 	req types.RequestApplySnapshotChunk) (*types.ResponseApplySnapshotChunk, error) {
 	reqres := cli.queueRequest(types.ToRequestApplySnapshotChunk(req))
-	cli.FlushSync()
+	if err := cli.FlushSync(); err != nil {
+		return nil, err
+	}
 	return reqres.Response.GetApplySnapshotChunk(), cli.Error()
 }
 
@@ -500,5 +502,7 @@ func (cli *socketClient) stopForError(err error) {
 	cli.mtx.Unlock()
 
 	cli.Logger.Error(fmt.Sprintf("Stopping abci.socketClient for error: %v", err.Error()))
-	cli.Stop()
+	if err := cli.Stop(); err != nil {
+		cli.Logger.Error("Error stopping abci.socketClient", "err", err)
+	}
 }

abci/tests/test_app/main.go

@@ -59,15 +59,26 @@ func testCounter() {
 	if err := cmd.Start(); err != nil {
 		log.Fatalf("starting %q err: %v", abciApp, err)
 	}
-	defer cmd.Wait()
-	defer cmd.Process.Kill()
+	defer func() {
+		if err := cmd.Wait(); err != nil {
+			log.Printf("error while waiting for cmd to exit: %v", err)
+		}
+
+		if err := cmd.Process.Kill(); err != nil {
+			log.Printf("error on process kill: %v", err)
+		}
+	}()
 
 	if err := ensureABCIIsUp(abciType, maxABCIConnectTries); err != nil {
 		log.Fatalf("echo failed: %v", err)
 	}
 
 	client := startClient(abciType)
-	defer client.Stop()
+	defer func() {
+		if err := client.Stop(); err != nil {
+			log.Printf("error trying client stop: %v", err)
+		}
+	}()
 
 	setOption(client, "serial", "on")
 	commit(client, nil)