Migrate the creation of runit control files from stage 1 script to core-services

[sbromberger]

This change allows later customization of the runit control files (/run/runit/stopit, et al.) via core-services instead of having to override in /etc/rc.local. This is an enabler of a solution to lxc/lxc-ci#408, discussed also in #50.

This PR will make the following (nonbreaking) change to the startup process: currently the runit control files are created AFTER the dmesg chmod in 1. Because core services are executed before the dmesg chmod, this means that the runit control files will be created BEFORE the dmesg chmod. Since runit and dmesg are independent, this should not cause any issues. (A separate question is whether we should move the dmesg work into core services, thus making 1 just a simple executor of core services.)

After this change, folks using lxd or incus containers will be able to create their own lower-priority core service to modify the permissions on the files to enable proper shutdown/reboot of the containers. These core services will survive upgrades to void-runit, unlike the current approach in the container script.

[leahneukirchen]

sounds reasonable, also the dmesg could be moved into a 97-dmesg.sh or so.

[sbromberger]

sounds reasonable, also the dmesg could be moved into a 97-dmesg.sh or so.

That would work too, but if we wanted to keep the ordering of the things as-is we'd need the dmesg stuff to come before the runit stuff.

[leahneukirchen]

The order of runit and dmesg is irrelevant, but e.g. dmesg should happen after 02-udev.sh