loader: poweroff() if cpus.size()>max_cpus

This patch fixes the case of silently hanging of OSv when >64 cpus are
provided.

Signed-off-by: Jaspal Singh Dhillon <jaspal.iiith@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
mgmt: update to latest

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>