This patch adds provider driver support to the Octavia v2
Listener API.
This patch also creates a provider driver for Octavia, fully
implementing the listener methods.
This patch also corrects the basic cookbook example for adding SNI
certificates to a listener.
Follow on patches will implement the remain parts of the API.
Story: 1655768
Task: 5165
Depends-On: https://review.openstack.org/492311
Change-Id: I386097197f51d94b34f9a7fd7af7b36238294faf