Up until today, Qubes OS would insist on either masking or disabling
or activating units that should get their state properly changed
but only on first package install (when the template is built).
This commit adds the possibility of having two types of unit presets:
* Initial presets: these are only changed state during first package
installs.
* Upgrade presets: these get their state changed during first
package installs as well as during upgrades.
All the maintainer has to do is abide by the instructions in the
preset file. Nothing else is necessary.
Namely, this allows users to enable SSHD on their templates or
standalone VMs and still keep it enabled even after the
qubes-core-vm-systemd package is upgraded.
Matt really wanted that, and so did I, so now we can do it!
:-)
There were multiple problems with reusing existing one:
- need to sync with upstream changes (configuration path etc)
- conflicts resolution on updates
- lack of iptables --wait, which causes firewall fail to load sometimes
QubesOS/qubes-issues#1067
