api: add serial console API calls v2.1/v3

This is a followup patch to:
api: add serial console API calls v2
    (https://review.openstack.org/#/c/113966/)
To add missing v3 APIs

Change-Id: I56a045d9b690ea36753513575a2023582da58e42
Patial-Implements: blueprint v2-on-v3-api
Merge "api: add serial console API calls v2.1/v3"