Add ingress controller

[kyv]

Please consider this pull-request which adds an nginx-ingress-controller to kubernetes. This pull-request is dependent on #43 and #44 but I thought you'd like to have those separated out as they may be useful without this one. Specifically this pull-request includes the following changes:

• allow opt-in scheduling on master node
• move api-server to port 6443 (so ingress-controller can handle ssl)
• add nginx-ingress-controller and assign to master node
• replace microbot with nginxdemos/hello
• open ports 80 and 6443 on master node
• close port 80 on workers

I think nginxdemos/hello makes more sense than microbot in this scenario because it demonstrates the function of the load balancer.

[andrewsykim]

@kyv I'll review this once the other 2 PRs go in :)