Commit 5153dcda80 removed bdm v2-only
request parameters to pass nova api v2.1 schema validation, but also
removed the ability to boot with legacy bdm specifying volume_id only.
This adds volume_id back to the request for legacy bdm when
no other parameters are specified.
Closes-Bug: #1501435
Conflicts:
novaclient/tests/functional/test_servers.py
Change-Id: Ie8c56c28492793990ef7ed6dc54768cef9e28a98
(cherry picked from commit abd0630bad)