cmd/serve: add serve docker command (#5415)

Fixes #4750

Co-authored-by: Ivan Andreev <ivandeex@gmail.com>

cmd/serve/docker/systemd.go

@@ -0,0 +1,17 @@
+// +build linux,!android
+
+package docker
+
+import (
+	"os"
+
+	"github.com/coreos/go-systemd/activation"
+	"github.com/coreos/go-systemd/util"
+)
+
+func systemdActivationFiles() []*os.File {
+	if util.IsRunningSystemd() {
+		return activation.Files(false)
+	}
+	return nil
+}