pmxcfs: allow read access for www-data to /run dir

pmxcfs: allow read access for www-data to /run dir

There's no real sensible information here, and we naturally only
allow read, but no write/exec.

This makes our IPCC restart connection re-cachin heuristic also work
for processes run as www-data, e.g., pveproxy, and thus guarantee a
more seamless pmxcfs restart - e.g., for package updates.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>