Add support for creating provider networks

Implements blueprint neutron-provider-networking

Change-Id: I4bad9483b92875ea5e143b0e11652e01faed35a4
Update readme.md, heat is now enabled by default

Change-Id: Ia36879711aa440f4fba657159afeba2105c6aae4
Merge "Update readme.md, heat is now enabled by default"
Merge "Add support for creating provider networks"
Merge branch 'master' of https://github.com/openstack-dev/devstack