Revise entropy check to work without floating IP

[mbuechse]

Floating IPs are not viable for every provider. It might be possible to do without them, as follows:

• include necessary commands in cloud-init, see https://github.com/osism/openstack-simple-stress/blob/main/openstack_simple_stress/main.py#L275
• parse console output as provided by Nova, see https://github.com/osism/openstack-simple-stress/blob/main/openstack_simple_stress/main.py#L208