Improve network support in launch-node.py

Currently launch-node.py doesn't allow to specify network label
and floating IP pool name, using the defaults from nova-network.

This patch allows to specify network label to attach instance to,
and floating IP pool from which floating IPs could be assigned.

Change-Id: I46024bc1c217f99f19717aeb04d424a01440203a
Merge "Improve network support in launch-node.py"