This patch adds a "volume_targets" DB table in order to save
the volume target information of physical nodes. With this patch,
Ironic can put/get volume target information to/from the database.
Co-Authored-By: Stephane Miller <stephane@alum.mit.edu>
Co-Authored-By: Ruby Loo <ruby.loo@intel.com>
Change-Id: I79063f9d0aafd7b740785a883732536704e43b7c
Partial-Bug: 1526231