add standard attributes to all BGPVPN resources

[Thomas Morin]

We need to add standard attributes to all BGPVPN resources.

Beyond the generic usefulness of 'description', tags, 'created_at' and 'updated_at', the 'revision' field which is part of standard attributes will be very useful to enforce consistency between the BGPVPN service plugin and its backends:
- when the backend is the bagpipe-based reference drivers, the revision fields allow the agent to detect and discard stale updated
- when the backend is an SDN controller that needs to sync the neutron-side DB with its own DB, the revision number can help design solutions (see for instance [1] and [2])

[1] https://etherpad.openstack.org/p/neutron-ptg-rocky ("Database synchronization between Neutron and SDN/External databases")
[2] https://docs.openstack.org/networking-ovn/latest/contributor/design/database_consistency.html#proposed-change

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/558741
Committed: https://git.openstack.org/cgit/openstack/networking-bgpvpn/commit/?id=14198baf6ca8f4efe05feca0dd7633adc3128ce4
Submitter: Zuul
Branch: master

commit 14198baf6ca8f4efe05feca0dd7633adc3128ce4
Author: Thomas Morin <email address hidden>
Date: Wed Apr 4 10:06:41 2018 +0200

    DB models: add standard attributes

    Beyond their intrinsic marginal usefullness, standard
    attributes [1] also include a revision number that helps
    avoid some races in OVO-based RPCs for resource updates.

    This changes adds standard attributes for the BGPVPN model
    and Net/Router/Port Association models.

    Note that this change adds something that had been missing
    since the removal of toosl/tox_install.sh: having 'neutron'
    as a required-project for the functional job. Not having
    it, resulted in the use of stable/queens neutron which test
    DB migration up to queens, but not any migration script
    defined for rocky.

    [1] https://docs.openstack.org/neutron/pike/contributor/internals/db_layer.html#the-standard-attribute-table

    Partial-Bug: 1765391
    Depends-On: I7630aab5e4f38d0fba862adc2426d4a7ca04a679
    Change-Id: I77ce46c0f33e2a366076d51ce6586fb3008dc6b1