Comment 0 for bug 1616422

Rationale: For backporting snapd to 14.04 LTS, we need to provide systemd's service manager (not just logind and auxiliary services like logind or timesyncd). upstart will continue to do the actual booting, and systemd will act as a "deputy init" which by default does not ship with/start any services by itself. We will only support this on server (at the first iteration at least), not on desktops.

Regression potential: This is a new binary package in universe, so existing systems are unaffected (provided that we ensure that the other binary packages do not change and there are no code changes that affect processes other than the "deputy pid 1" service manager). So for plain upgrades the regression potential is very low. However, there is a medium potential for breakage when actually installing the new systemd package, as it might interfere with upstart jobs or other running processes, cause boot/shutdown hangs, etc.

Test plan:
 1. Dist-upgrade a trusty installation to the proposed versions. Ensure this does not pull in "systemd", and that booting, shutdown, desktop startup, suspend on lid close, resume, logout, and user switching all still work.

 2. Install the "systemd" binary package (this will replace/remove systemd-shim). Verify that you can talk to the service manager with "sudo systemctl status". Check that booting and shutdown continues to work without (significant) delays.

 3. Install a package that ships a systemd .service file, such as "haveged". Ensure that the service file is ignored, "pgrep -af haveged" should only have *one* process and "systemctl status haveged" should not be running (it should not exist, or not be enabled and be inactive).

 4. Install snapd (not in trusty yet, e. g. from Thomas' PPA) and ensure you can install a snap, and its services start after installing the snap and after rebooting.

 5. Dist-upgrade to 16.04 to ensure that there are no file conflicts, dependency issues, etc.