Fix v3 extensions inherit from wrong controller

Extensions keypairs and config_drive's controller should
inherit from nova.api.openstack.wsgi.Controller. Inherit
from wrong controller may cause strange errors.

Partially implements bp v3-api-extension-versioning

Change-Id: I5e2a588960bf6b1c0afafb89ecaab255dbd2a1f4
Merge "Fix v3 extensions inherit from wrong controller"