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