OSP13: Workaround BZ#1543580 - FORWARD DROP on UC
OSP13: Workaround BZ#1543580 - FORWARD DROP on UC

With at least osp13 on rhel-7.5 there is issue
of traffic forwarding being blocked on undercloud,
which effectively cuts non-api overcloud nodes from dns,
and so delays any ssh connections (like ceph ansible)
so much they timeout (due to sshd doing reverse dns lookup).

Change-Id: I70ea1467d953577925bca84e26da4c0529f070ae

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