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 commit 'refs/changes/83/86083/2' of git://gold.eng.hq.xensource.com/git/github/openstack-dev/devstack into tmpbranch