Fix env variable KUBERNETES_PUBLIC_ADDRESS

[alban]

Symptoms:

$ echo $KUBERNETES_PUBLIC_ADDRESS
kubernetes-the-hard-way

With this patch, I get the IP address instead of the name.

[alban]

Oops I missed the discussion in #299 and #282 that says it works both ways anyway.

Since $KUBERNETES_PUBLIC_ADDRESS is the IP in other part of the doc, including in the same file, I think it's better to use the IP though.

[kelseyhightower]

I'll now use address everywhere to avoid confusion. This is fixed on the 1.10.2 branch.