Various iptables integration fixes

* oo-diagnostics will warn if /etc/sysconfig/iptables is missing
* oo-diagnostics will advise admins not to use lokkit (and offer helpful advice
  if they must)
* oo-admin-ctl-iptables-port-proxy will ensure the rhc-app-comm chain exist
* oo-admin-ctl-iptables-port-proxy's status method was improved to better handle custom NAT rules

This is to address:

Bug 1032798 - unable to create scaled app because of misconfigured iptables method
Bug 1027122 - Running lokkit tools on node will block openshift-iptables-port-proxy service starting.
Bug 1053639 - Following deployment instructions for OSE2.0 node seems to cause iptables issues with openshift-iptables-port-proxy service start

The latter has been very problematic because manual installs would tell users
to run a sed command.  If commands are copied wrong or out of order it can lead
to a broken setup.  Lokkit commands are much easier to copy/paste from a wiki.