change namespace to live under 'ncflex'

This changes nova-compute-flex from providing a 'nova' module to providing a ncflex module with
ncflex.nova.virt.flex under that.

I believe that if packaging were to install the nova/virt/flex under nova/virt of the nova compute-common, then you could do:
   compute_driver = nova.virt.flex.LXCDriver

The one place that the string 'ncflex' is exposed here is in 
ncflex/nova/virt/flex/containers.py.  in the vif_driver .  that is somewhat annoying.
I do not know how to get a relative import on that.