Use db unique index to control duplicate name for NFV resources

[yong sheng gong]

Problem:
Currently, we are using python code to avoid name duplication of a certain resource type:
such as:
https://github.com/openstack/tacker/blob/master/tacker/vnfm/plugin.py#L154
        if self._get_by_name(context, vnfm_db.VNFD, name):
            raise exceptions.DuplicateResourceName(resource='VNFD', name=name)

this cannot work if there are multiple tacker servers running where the race condition will happen.

solution:
    to use unique index on tenant_id and name columns of the NFV resources.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/439719

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/450528

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/439719
Committed: https://git.openstack.org/cgit/openstack/tacker/commit/?id=8b517c0029af1390717726ebe77aefc4ad5a2012
Submitter: Jenkins
Branch: master

commit 8b517c0029af1390717726ebe77aefc4ad5a2012
Author: Kanagaraj Manickam <email address hidden>
Date: Wed Mar 1 12:52:49 2017 +0530

    Adds unique constraint on name and tenant_id

    Update the schema for VIM, VNFD, VNF, NS and NSD tables
    to constraint the name per tenant as unique.

    Change-Id: I463fe02ebd4b0f720260bda1c3da4cdebc6ec238
    Closes-bug: #1667641

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/tacker 0.8.0 release.

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Kanagaraj Manickam <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/tacker/+/450528