Use floating ip in VM runcommand scenario

Currently the VM runcommand scenario use the fixed ip to ssh connect to the instance.
This could only works if fixed ip range is directly accessible with is the case in very limited deployments.

This blueprint proposes to support attachment of a floating ip to the instance allowing connection in most deployments.

Floating ips management requires to modify current scenario parameters:
    - Currently the network used to connect to the instance is referred as "network".
    - The concept of fixed and floating network should be introduced: parameter "network" will be renamed in "fixed_network" and parameter "floating_network" will be added.
    - To maintain compatibility with current implementation, a new parameter "use_floatingip" will be added. This parameter will be defaulted to "true" as the use of floating ips is generally preferred.

def boot_runcommand_delete(self, image_id, flavor_id,
         script, interpreter,
         fixed_network='private',
         floating_network='public',
         username='ubuntu', ip_version=4,
         port=22, use_floatingip=True, **kwargs):