Get Me a Network

This is the nova side of the neutron get-me-a-network spec:

http://specs.openstack.org/openstack/neutron-specs/specs/liberty/get-me-a-network.html

With changes:

https://review.openstack.org/#/q/topic:bp/get-me-a-network,n,z

The main idea for the nova changes is:

1. User requests to create an instance and doesn't provide any network information in the create request.
2. When allocating network information for the instance:
  a) if a network is not provided and
  b) the project does not have access to a private network or a public shared network and
  c) the neutron auto-allocate-topology extension is enabled then
  d) Nova will request neutron to auto-allocate the network which nova will then use to associate with the instance (a port will be created by nova in the auto-allocated network).

A microversion will be added to the nova REST API to signal this change.

TBD: with the microversion, does nova default to auto-allocate the network and the user has to opt out of that if they don't want a network on the initial instance create, or does the user have to specify if they want a network auto-allocated? To be answered in the spec discussion and/or nova meeting on 2/18.

See the mailing list discussion on the microversion question:

http://lists.openstack.org/pipermail/openstack-dev/2016-February/086437.html

Dependencies:

1. The auto-allocate-topology REST API in neutron (merged in mitaka)
2. python API bindings in python-neutronclient for the auto-allocate-topology API (WIP)
3. devstack changes to setup the default public network and subnets: https://review.openstack.org/#/c/277683/10/neutron/tests/api/admin/test_auto_allocated_topology.py