I'm not certain if this is related but this patch was made post newton: https://review.openstack.org/#/c/422175/
Brent is correct, the newer version of Octavia refers to using octavia-db-manage. Once correct connection string is set in /etc/octavia/octavia.conf, alembic migrations succeed.
I also needed to change localhost address in the config to use node's IP address as mysql doesn't listen on localhost. Maybe worth updating document from comment 0.