This function is different from panel_util_get_icon_for_uri(), but
hopefully it will provide similar results. Known differences:

- no longer returns special icon for `x-nautilus-search` uri and
at least in last two major versions nautilus crashes when used with
this uri - nautilus#234.

- no longer returns special icon for `burn` uri, seems that returned
icon `nautilus-cd-burner` does not exist.