Add ability to import from Neutron DB

[Shachar Snapiri]

Currently the only install type we support is a clean install (and soon also upgrade from older DragonFlow version).
A capability we still lack is the ability to integrate into an existing setup, thus getting the current running configuration from neutron and setting it into the DragonFlow DB, and continue to function as part of the system with no downtime (or as little as possible).
This is required both for the above-mentioned scenario, but also for users who would like to migrate from the Neutron reference implementation to using DragonFlow.

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: master
Review: https://review.openstack.org/532788

[Irena Berezovsky (irenab)]

I think the initial condition of the neutron DB should be defined in more details.
Is there already existing network configuration, what is the initial plugin responsible for Neutron DB was population. Do we assume ML2 plugin? What are enabled mechanism drivers? Does it matter?

[Omer Anson (omer-anson)]

Planned for Queens (If we make it)

[OpenStack Infra (hudson-openstack)]

Change abandoned by Sean McGinnis (<email address hidden>) on branch: master
Review: https://review.opendev.org/532788