systemd: get dbus connection directly in NewSystemdUnitManager

Let's get dbus connection directly inside NewSystemdUnitManager,
instead of calling a separate function createDbusConnection().

Suggested by @jonboulle.
See #1393 (comment)

systemd/manager.go

@@ -37,7 +37,13 @@ type systemdUnitManager struct {
 }
 
 func NewSystemdUnitManager(uDir string, systemdUser bool) (*systemdUnitManager, error) {
-	systemd, err := createDbusConnection(systemdUser)
+	var systemd *dbus.Conn
+	var err error
+	if systemdUser {
+		systemd, err = dbus.NewUserConnection()
+	} else {
+		systemd, err = dbus.New()
+	}
 	if err != nil {
 		return nil, err
 	}
@@ -60,13 +66,6 @@ func NewSystemdUnitManager(uDir string, systemdUser bool) (*systemdUnitManager,
 	return &mgr, nil
 }
 
-func createDbusConnection(systemdUser bool) (*dbus.Conn, error) {
-	if systemdUser {
-		return dbus.NewUserConnection()
-	}
-	return dbus.New()
-}
-
 func hashUnitFiles(dir string) (map[string]unit.Hash, error) {
 	uNames, err := lsUnitsDir(dir)
 	if err != nil {