Packstack Documentation for Stein

[psdnuxeo]

Some of the documentation for Packstack is out of date at these links:

https://www.rdoproject.org/networking/neutron-with-existing-external-network/

https://www.rdoproject.org/install/adding-a-compute-node/

Specifically,
Set CONFIG_NEUTRON_OVS_TUNNEL_IF=
should now be
Set CONFIG_NEUTRON_OVN_TUNNEL_IF=

There may be other outdated instructions related to OVS / OVN that I haven't hit on yet.

[amoralej]

fixed in #1281