This adds a setting (disabled by default) to have the browbeat
installation playbook add the value
UseDNS no
to the overcloud node sshd config, for the scale lab exspecially this
can result in a 4x or greater speed improvement running ansible playbooks.
Not quite ludicrous speed, that's going to require pipelining, but it will do
Change-Id: I660cfc5a815bd08337f71e2ed9f97252794b09e2
54d67eb1f1