use native golang SSH library but ssh-keygen when enable built-in SSH server to remove dependent on that command lines (#5976)

* use native golang SSH library but ssh-keygen when enable built-in SSH server to remove dependent on that command lines

* fix tests and add comment head

integrations/git_helper_for_declarative_test.go

@@ -12,20 +12,20 @@ import (
 	"net/http"
 	"net/url"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"testing"
 	"time"
 
 	"code.gitea.io/git"
 	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/ssh"
 	"github.com/Unknwon/com"
 	"github.com/stretchr/testify/assert"
 )
 
 func withKeyFile(t *testing.T, keyname string, callback func(string)) {
 	keyFile := filepath.Join(setting.AppDataPath, keyname)
-	err := exec.Command("ssh-keygen", "-f", keyFile, "-t", "rsa", "-N", "").Run()
+	err := ssh.GenKeyPair(keyFile)
 	assert.NoError(t, err)
 
 	//Setup ssh wrapper