implementations. When managing leases 4 abstract methos have been added
to the interface:
- from_vattr, to notify/request a new network from IPAM
- allocate_addr, to set an address as used
- get_addr, to request a free address
- free_addr, to set an address as unused
This commits also includes an AddressRange implementation based on
OpenNebula's internal IPAM
Signed-off-by: Ruben S. Montero <rsmontero@opennebula.org>