qemu: Load GTK modules/resources from chroot

We are running qemu that is installed in the chroot. The GTK framework needs to be configured to load resources from the chroot as well.

• The GTK menu icons will display properly
• Prevents errors like this when running qemu --display gtk.

(ld-musl-x86_64.so.1:13069): GdkPixbuf-WARNING **: 13:39:18.294: Cannot open pixbuf loader module file '/usr/lib/gdk-pixbuf-2.0/2.10.0/loaders.cache': No such file or directory

This likely means that your installation is broken.
Try running the command
  gdk-pixbuf-query-loaders > /usr/lib/gdk-pixbuf-2.0/2.10.0/loaders.cache
to make things work again for the time being.

This can allow spice clients work if they are run from the chroot (related to #1728 (closed)). Some button icons are not shown but it doesn't crash anymore. I tested remote-viewer and spicy. It's not actually implemented in this patch though. It would need to be done separately.