Fix egress interfaces script to work on IPI clusters

We adjust the script to use the external API DNS record (api.) instead of api-int, so that it works without any problems on IPI clusters which provide the api-int record via in-cluster CoreDNS which isn't running yet before the kubelet is started.

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appuio / component-openshift4-nodes

Fix egress interfaces script to work on IPI clusters #87

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