oo-accept-node: Add check_ext_net_dev_addr

Add check_ext_net_dev_addr to oo-accept-node to check that the network
interface specified by EXTERNAL_ETH_DEV in /etc/openshift/node.conf has
a globally scoped IPv4 address (if it does not, oo-iptables-port-proxy
will fail).

This commit fixes bug 1121206.
Merge pull request #5623 from Miciah/bug-1121206-oo-accept-node-add-check_ext_net_dev_addr

Merged by openshift-bot