Honor disable_fsync during checkout also

Finally, fsync to ensure all entries are on disk, unless disabled.
 We support disabling this for cases like server-side buildroot
 construction where we don't need to be robust against power loss

src/libostree/ostree-repo-checkout.c

@@ -661,11 +661,14 @@ checkout_tree_at (OstreeRepo                        *self,
    * this should be configurable for the case where we're constructing
    * buildroots.
    */
+  if (!self->disable_fsync)
+    {
     if (fsync (destination_dfd) == -1)
       {
         ot_util_set_error_from_errno (error, errno);
         goto out;
       }
+    }
 
   ret = TRUE;
  out: