In Arista ML2 delete tenant if no resources associated with it

[Sukhdev Kapur]

When all resources for a tenant are deleted (ports and networks), the tenant is removed Arista's DB. This operation is performed during port/network_delete_precommit() operation. Arista's ML2 Sync mechanism used to ensure that the tenant is deleted from the back-end (i.e from Hardware) as well.

With enhancements to the Sync mechanism to accommodate large scale deployments, it is prudent to move the deleting of tenant from port/network_delete_precommit() to port/network_delete_postcommit(). This ensures that the tenant is immediately deleted from the DB as well as the back-end and removes the dependency on the sync mechanism.

This bug is to make this fix.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/162778
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=1ec7c542116f4980ee6680adf261d9a29c5a1d61
Submitter: Jenkins
Branch: master

commit 1ec7c542116f4980ee6680adf261d9a29c5a1d61
Author: Sukhdev <email address hidden>
Date: Mon Mar 9 14:45:21 2015 -0700

    In Arista ML2 delete tenant without any resources

    If there are no resources associated with a
    tenant, it was deleted from Arista DB in
    delete_xxx_precommit() methods. The sync
    mechanism used to make sure that back-end is in
    sync with DB.

    Lately, the sync mechanism has been enhanced to
    support scaled deployment. Therefore, the
    delete_tenat() call now needs to be invoked from
    delete_xxx_postcommit() methods instead of
    delete_xxx_precommit() methods. Additionally,
    when the tenant is removed from the DB, it is
    removed from the back-end as well. This removes
    the dependancy on the sync mechanism to take
    care of this.
    [Note: Sync will still do it, but, this way it
    gets done right away]

    Closes-bug: 1429968
    Change-Id: I2f6ddb01079fe4e2648685ca97d0be06db2d1a55