Handle empty array in update.sh

Fixes #1776
Break out dynamic salt files to enable clean kube-push.

This lets us blow away salt files and replace them with a new version while keeping a tree of "overlay" files that are cluster specific and generated at cluster up time.

Fixes #1783
Merge pull request #1787 from jbeda/e2e-fix

Fix kube-push
Create MinionController to sync minions from cloudprovider (pkg cloudprovider/controller).
Remove OnceAndForever util, create a Run() method on MinionController.