shill: vpn: Implement NSS database interface class.

Use the NSS class to lookup NSS certificates for OpenVPN.

BUG=chromium-os:28792
TEST=unit tests

Change-Id: I2e0c7924d664f375f5b01bc73506e2b91e6f8720
Reviewed-on: https://gerrit.chromium.org/gerrit/19457
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Ready: Darin Petkov <petkov@chromium.org>
diff --git a/glib.h b/glib.h
index 6f75048..079b244 100644
--- a/glib.h
+++ b/glib.h
@@ -145,6 +145,17 @@
                                           GError **error);
   // g_spawn_close_pid
   virtual void SpawnClosePID(GPid pid);
+  // g_spawn_sync
+  virtual gboolean SpawnSync(const gchar *working_directory,
+                             gchar **argv,
+                             gchar **envp,
+                             GSpawnFlags flags,
+                             GSpawnChildSetupFunc child_setup,
+                             gpointer user_data,
+                             gchar **standard_output,
+                             gchar **standard_error,
+                             gint *exit_status,
+                             GError **error);
   // g_strfreev
   virtual void Strfreev(gchar **str_array);
   // g_type_init