[config] skip directories while loading config

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[server] run statefs as system

Option --system changes default used configuration directory to the
system one

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[systemd] statefs system service

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>