<openshift.ks> Override EXTERNAL_ETH_DEV in node.conf if needed

If CONF_INTERFACE/interface is specified override EXTERNAL_ETH_DEV in
node.conf.

refactor iface to interface to match variable/parameter naming
conventions
Merge pull request #370 from detiber/fixNodeInterface

<openshift.ks> Override EXTERNAL_ETH_DEV in node.conf if needed