Add an echo client to be used instead of nc.

nc behaviour depends on the implementation version of what's on the current host.
Here we use our own client with stable behaviour.

Signed-off-by: Federico Paolinelli <fpaoline@redhat.com>

pkg/testutils/echo/client/client.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"net"
+)
+
+func main() {
+	target := flag.String("target", "", "the server address")
+	payload := flag.String("message", "", "the message to send to the server")
+	flag.Parse()
+
+	if *target == "" || *payload == "" {
+		flag.Usage()
+		panic("invalid arguments")
+	}
+	conn, err := net.Dial("tcp", *target)
+	if err != nil {
+		panic(fmt.Sprintf("Failed to open connection to [%s] %v", *target, err))
+	}
+	defer conn.Close()
+
+	_, err = conn.Write([]byte(*payload))
+	if err != nil {
+		panic("Failed to send payload")
+	}
+	_, err = conn.Write([]byte("\n"))
+	if err != nil {
+		panic("Failed to send payload")
+	}
+
+	buf := make([]byte, 4)
+	for {
+		n, err := conn.Read(buf)
+		fmt.Print(string(buf[:n]))
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			panic("Failed to read from socket")
+		}
+	}
+}