procd: improve status reporting for partially running services

procd: improve status reporting for partially running services

The existing implementation incorrectly reported `running` for services
without any instances or with all instances stopped/terminated.

Improve the default implementation of `/etc/init.d/* status` to properly
report services with not running instances. In case a service exists,
but without running instance, the status call will now report
"not running" with exit code 5. In case some instances are running and
some are stopped/terminated, the call will report "running (X/Y)" where
`X` denoted the amount of running instances and `Y` the amount of total
registered ones.

Ref: https://forum.openwrt.org/t/x/159443
Signed-off-by: Jo-Philipp Wich <jo@mein.io>