systemd support

[marcosps]

I'm sure that this was already being requested, but I couldn't find any issues opened/closed about it, or a discussion. And I'm also sure that this can be useful for more people, so I'm leaving a discussion open about it :)

For my usecase, I'm currently using virtme-ng to test reproducer for CVEs for different kernels. My workflow is that I have a more then 60 downloaded kernels, and I use vng to boot these kernels and run scripts to check if the kernels are vulnerable or not. It works nicely, even on different architectures. The issue is that sometimes I need to start services using systemctl, so a error message appears:

System has not been booted with systemd as init system (PID 1). Can't operate.

Just my 2 cents :)