Adds lock server extension for V3 API

Moves the lock/unlock server functionality out of admin_actions into
its own extension. This part of the larger
blueprint v3-api-admin-actions-split allows more selective enablement of
features contained in the admin actions extension.

Some setup work is done in the tests directory with an
admin_only_action_common.py file. This allows tests which are
split out from test_admin_actions (as their corresponding features
are separated from the admin_actions extension) can continue to
share code.

Note that XML api samples are no longer generated because
bp remove-v3-xml-api has been approved.

Partially implements bp v3-api-admin-actions-split
DocImpact: Adds os-lock-server extension and moves lock/unlock
functionality out of os-admin-actions into this new extension

Change-Id: Ie4b6e856c2f5c33de5575aa8666e0b2784b58d05
Merge "Adds lock server extension for V3 API"