Remove H307 no db in virt

This is a Nova only rule that shouldn't be in the generic hacking tool

Change-Id: Ibdba7319a1bf08fb917aaac8503203a857f08b83
Reviewed-on: https://review.openstack.org/27090
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Doug Hellmann <doug.hellmann@dreamhost.com>
Reviewed-by: Doug Hellmann <doug.hellmann@dreamhost.com>
Tested-by: Jenkins