Set hosts user for all undercloud hosts
Set hosts user for all undercloud hosts

When running infrared against an [undercloud] group
that has more than one host, the Ansible "add_host"
directive by design will only run against one of those hosts,
as it runs outside of the playbook loop.  Per Ansible
documentation, add a "with" loop against all hosts
in the "undercloud" group so that all undercloud entries
in the inventory are updated.

I'm not sure this approach is entirely correct in the case
where the --limit parameter is used with ansible as well
to limit activity to a subset of undercloud hosts,
if this directive should also take that into account (or
if "groups" already does that).

Change-Id: I9f570ef1a7a2dbdd20f78e9daf8a70990e571995

redhat-openstack/infrared,redhat-openstack/infrared,redhat-openstack/infrared