On dbus we have two apis: one for registering a new machne when the
client already has a cgroup (RegisterMachine()) and one where it doesn't
and machined shall create it (CreateMachine()).
Let's add the same for the varlink api. To simplify things we just
implement it via a boolean flag to the existign RegisterMachine()
varlink call, since the differences are mostly minor otherwise.
Lennart Poettering
f98e821cda