Switch NeonVMs to systemd

[sharnoff]

Problem description / Motivation

There's a few reasons why we might want to switch to using systemd:

1. Better lifecycle management for "daemons", which may help with Epic: Unify vm-builders #577
2. Ability to use preexisting logging infrastructure like journalctl, for Epic: Separately tagged logs for VM processes, dmesg, and runner  #578
3. It's a more "standard" init system, so should hopefully make NeonVM easier to hack on and maintain

DoD

NeonVMs use systemd as the init system.

Implementation ideas

This probably also involves switching where we get all the binaries and shared libs — currently those are from alpine, but switching to debian would probably make this much easier. Relevant code is here:

autoscaling/neonvm/tools/vm-builder/files/Dockerfile.img

Lines 19 to 51 in 8a91e83

	# add udevd and agetty (with shared libs)
	RUN set -e \
	&& apk add --no-cache --no-progress --quiet \
	acpid \
	udev \
	agetty \
	su-exec \
	e2fsprogs-extra \
	blkid \
	flock \
	&& mv /sbin/acpid /neonvm/bin/ \
	&& mv /sbin/udevd /neonvm/bin/ \
	&& mv /sbin/agetty /neonvm/bin/ \
	&& mv /sbin/su-exec /neonvm/bin/ \
	&& mv /usr/sbin/resize2fs /neonvm/bin/resize2fs \
	&& mv /sbin/blkid /neonvm/bin/blkid \
	&& mv /usr/bin/flock /neonvm/bin/flock \
	&& mkdir -p /neonvm/lib \
	&& cp -f /lib/ld-musl-x86_64.so.1 /neonvm/lib/ \
	&& cp -f /lib/libblkid.so.1.1.0 /neonvm/lib/libblkid.so.1 \
	&& cp -f /lib/libcrypto.so.1.1 /neonvm/lib/ \
	&& cp -f /lib/libkmod.so.2.3.7 /neonvm/lib/libkmod.so.2 \
	&& cp -f /lib/libudev.so.1.6.3 /neonvm/lib/libudev.so.1 \
	&& cp -f /lib/libz.so.1.2.12 /neonvm/lib/libz.so.1 \
	&& cp -f /usr/lib/liblzma.so.5.2.5 /neonvm/lib/liblzma.so.5 \
	&& cp -f /usr/lib/libzstd.so.1.5.2 /neonvm/lib/libzstd.so.1 \
	&& cp -f /lib/libe2p.so.2 /neonvm/lib/libe2p.so.2 \
	&& cp -f /lib/libext2fs.so.2 /neonvm/lib/libext2fs.so.2 \
	&& cp -f /lib/libcom_err.so.2 /neonvm/lib/libcom_err.so.2 \
	&& cp -f /lib/libblkid.so.1 /neonvm/lib/libblkid.so.1 \
	&& mv /usr/share/udhcpc/default.script /neonvm/bin/udhcpc.script \
	&& sed -i 's/#!\/bin\/sh/#!\/neonvm\/bin\/sh/' /neonvm/bin/udhcpc.script \
	&& sed -i 's/export PATH=.*/export PATH=\/neonvm\/bin/' /neonvm/bin/udhcpc.script

(and, maybe this could be easier by just chroot + install? or, it'll be much easier if we're running proper containers inside the VM, because then we don't need to worry about isolating host files)

[Omrigan]

We should research if systemd can be used to startup containers inside the VM.

Alternative approach is to use CoreOS