hostinfo: fix earlier git fail, add files lost in move

This was meant to be part of 47045265b9
which instead deleted them :(

Updates tailscale/corp#1959

hostinfo/hostinfo_test.go

@@ -0,0 +1,29 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package hostinfo
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestNew(t *testing.T) {
+	hi := New()
+	if hi == nil {
+		t.Fatal("no Hostinfo")
+	}
+	j, err := json.MarshalIndent(hi, "  ", "")
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Logf("Got: %s", j)
+}
+
+func TestOSVersion(t *testing.T) {
+	if osVersion == nil {
+		t.Skip("not available for OS")
+	}
+	t.Logf("Got: %#q", osVersion())
+}