Adds agent support for Nova V3 API

Adds support and tests for the os-agents extension
for the Nova V3 API

Partially implements blueprint v3-api

Change-Id: I53f8a1cbab6f4dee10fb823bc51ae90baa97fa7a
Remove commands not supported by Nova V3 API

Remove commands which are no longer supported by the Nova
V3 API and that we will definitely not be proxying to another
service. Removes:

- cloudpipe-list
- cloudpipe-create
- cloudpipe-configure
- coverage-start
- coverage-stop
- coverage-report
- coverage-reset

Partially implements blueprint v3-api

Change-Id: I366cd0233977c1b506d55de280188ecccda8188f
Stop using deprecated keyring backends

keyring.backend.* was deprecated in python-keyring 1.1 and we already
require keyring 1.6.1. This also makes novaclient compatible with python-keyring 3.0
which removes the deprecated paths.

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=728470#10.

Change-Id: I4919ac515e589fddc6044c0cd2f4cbc06c2ec91f
Co-Authored-By: Sebastian Ramacher <sramacher@debian.org>
Merge "Stop using deprecated keyring backends"
Merge "Adds agent support for Nova V3 API"
Merge "Remove commands not supported by Nova V3 API"