Hotfix: add user lighttpd settings

Problem

Commit turris/webapps@62b7c02e that fixes changes from merge request !872 (merged) does not affect shield devices, as Shield does not have webapps package

Solution

Add to (config that is to shield only) lighttpd-reforis-only.conf following code:

server.username  := ""
server.groupname := ""

@gstrauss