Run os-net-config on step 3
Run os-net-config on step 3

In some cases such as RHEL7>RHEL8 upgrade leapp or NetworkManager may
change resolv.conf. This patch invokes os-net-config on step3 to ensure
that network parts are configured properly (interfaces, resolv.conf).
Since os-net-config is idempotant it causes no harm or packet loss to
undercloud.

Change-Id: I0b2f28cd3d92795802e51c69d975826af0ee86ee
Resolves: rhbz#1870617

openstack/tripleo-heat-templates,openstack/tripleo-heat-templates