neutron db migration is skipped when DB current version is None.

[Xu Han Peng]

Neutron DB schema auto-generation has been removed by this patch:

https://review.openstack.org/#/c/40296/

DB migration is the only way to generate Neutron DB schema.

In neutron cookbook code:
https://github.com/stackforge/cookbook-openstack-network/blob/master/recipes/server.rb#L54

DB upgrade is always skipped when current version is None, which lead to later neutron server problem due to tables are missing.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/123048

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/123048
Committed: https://git.openstack.org/cgit/stackforge/cookbook-openstack-network/commit/?id=41a8b0d73fa3965c5a47d1c5b74567e21e646e6a
Submitter: Jenkins
Branch: master

commit 41a8b0d73fa3965c5a47d1c5b74567e21e646e6a
Author: Xu Han Peng <email address hidden>
Date: Mon Sep 22 13:34:17 2014 +0800

    Remove Neutron DB stamp and upgrade to head

    Neutron DB schema auto-generation has been removed
    by this patch:
    https://review.openstack.org/#/c/40296/

    We should remove DB stamp and upgrade to version "head"
    each time, no matter it's first time deployment or run
    by many times.

    Change-Id: I74f6dc76091d6c7988b680eec16900bef3f3f61c
    Closes-Bug: #1372260