Fix the format of scamper command argument (#111)

* Fix the format of scamper command argument

The flags that are passed to scamper's command (e.g., tracelb) via
the -I flag should be specified as one string argument.	Quotes are
only needed when using the shell or printing log messages.

Tests:
    - go test ./...
    - docker-compose uy (tracetool=scamper)
      docker exec -it trc_traceroute-caller_1 apt-get update
      ...
      scamper.go:134: Trace succeeded in context 0xc0000bd620
      ...

* Assign slice of args to a string variable

Author: Saied Kazemi

tracer/scamper.go

@@ -107,14 +107,14 @@ func (s *Scamper) trace(conn connection.Connection, t time.Time) (string, error)
 		tracelbCmd = append(tracelbCmd, []string{"-O", "ptr"}...)
 	}
 	tracelbCmd = append(tracelbCmd, conn.RemoteIP)
+	iVal := strings.Join(tracelbCmd, " ")
 	cmd := shx.Pipe(
-		shx.Exec(s.Binary, "-I", fmt.Sprintf("%q", strings.Join(tracelbCmd, " ")), "-o-", "-O", "json"),
+		shx.Exec(s.Binary, "-I", iVal, "-o-", "-O", "json"),
 		shx.Write(&buff),
 	)
 
 	// Now run the command.
-	log.Printf("Trace started in context %p (%s -I \"%s\" -o- -O json)\n",
-		ctx, s.Binary, strings.Join(tracelbCmd, " "))
+	log.Printf("Trace started in context %p (%s -I %q -o- -O json)\n", ctx, s.Binary, iVal)
 	start := time.Now()
 	err = cmd.Run(ctx, shx.New())
 	latency := time.Since(start).Seconds()

tracer/scamper_test.go

@@ -52,7 +52,7 @@ func TestScamper(t *testing.T) {
 	uuid, err := conn.UUID()
 	rtx.Must(err, "Could not make uuid")
 	expected := `{"UUID":"` + uuid + `","TracerouteCallerVersion":"` + prometheusx.GitShortCommit + `","CachedResult":false,"CachedUUID":""}
--I "tracelb -P icmp-echo -q 3 -W 0 -O ptr 10.1.1.1" -o- -O json
+-I tracelb -P icmp-echo -q 3 -W 0 -O ptr 10.1.1.1 -o- -O json
 `
 	if strings.TrimSpace(out) != strings.TrimSpace(expected) {
 		t.Error("Bad output:", out)