Fix working sahara with heat and nova-network

Uses OS::Nova::FloatingIP and OS::Nova::FloatingIPAssociation
heat resources for assignment floating ip

Added two unit tests:
* for nova-network with autoassignment floating ip
* for nova-network without autoassignment floating ip

Change-Id: I82a28759bc13992d765969ef8143bd364dc7cf2d
Closes-bug: #1259176
Merge "Fix working sahara with heat and nova-network"