Adds certificates support for Nova V3 API

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

Partially implements blueprint v3-api

Change-Id: I9a75bf04a7047af6c501af2df72de4b8ce3462b0
Adds keypairs support for the Nova V3 API

Adds support and tests for the keypairs extension for
the Nova V3 API. The V3 version of the keypair extension
has been made part of the core V3 API and as a result no longer
has the "os-" prefix in the url.

Differences between the V2 and V3 API are described here:
https://wiki.openstack.org/wiki/NovaAPIv2tov3

Partially implements blueprint v3-api

Change-Id: Id4a77e1e4565f63ecdf7753d3c224975519fc07c
Merge "Adds certificates support for Nova V3 API"
Merge "Adds keypairs support for the Nova V3 API"