Fail more gracefully when systemd is not running/PID 1

[sirredbeard]

/tmp/platform9-install-debian.sh requires systemd running as PID 1.

Provisioning on an instance without systemd or systemd as PID 1 does not fail until the certless-packages.yml task in pf9-hostagent role is executed.

Even then it requires the user to go read ~/pf9/log/..., go untar /tmp/platform9-log-bundle.tar.gz, and read that log.

I would suggest checking for systemd running as PID1 earlier in the provisioning process, in the common tasks, with a more descriptive error message if systemd is not running as PID 1.

This affects WSL as well as some Linux distros and container platforms that do not support systemd by default.