Rehome functions to enable Neutron's placement integration

Those functions were part of the neutron devstack plugin but we
discussed it during last PTG [1] and decided to move to the Devstack
repo as plugins which are used by e.g. CI jobs which are defined outside
of the neutron repository.
Placement integration is used e.g. in the tempest-slow job which is
defined in tempest and used by many different OpenStack projects.

[1] https://etherpad.opendev.org/p/neutron-yoga-ptg#L142

Change-Id: Ib86071881f16de1b69c0f9b1b19b6df8b7e66a07
2 files changed