The directory set as `lock_path` in `nova.conf` must be created with
the nova system user as its owner, otherwise the VIF plugin would fail
to acquire a lock when launching an instance.
Here we set up systemd to create this directory with correct owner and
permissions, besides moving its path to a `nova_lock_path` variable.
Apparently, the `/var/lock/{{ item.value.service_name }}` directory,
which is also created by `nova-systemd-tempfiles.j2`, is not needed at
all. But as this patch is intended to be backported to a stable release,
we keep it by now to avoid any unforeseen issues.
Change-Id: I9886778eddc23f0f71dfdfc87f4f715054946b3d
Closes-Bug: #1636604
1d4c3ad6ec