Use external_ip to populate the node address
Use the new external_ip inventory variable to populate node address.
Note that cluster_ip is still used if external_ip has not been set.
This makes it possible to connect to kubernetes apiserver using the external_ip
without disabling ssl cert verification.
As an added bonus, the inventory hostname is now used as the node name to make
node names more predictable.
Change-Id: I3cc25c488d68f2f858a5eb3438d96285fa7517ca
Issue-ID: OOM-2112
Signed-off-by: Michal Zegan <m.zegan@samsung.com>