In OpenDev, we use an inventory file with the public v4 and v6
addresses listed as hostvars. We would like to use that feature in
testing as well. In order to do that, we need to mutate the inventory
so that the public_ipv4 address supplied by nodepool is mapped to
the public_v4 address in the inventory. This additional option allows
the user to configure such mappings.
Change-Id: I48f03cacdf4531c42d33f6e807845d5c2a1da1d5
41d4d6c41d