Hyperkube from CoreOS now ships with all binaries required for
calico and flannel (but not weave). It simplifies deployment for
some network plugin scenarios to not download CNI images.
TODO: Optionally disable downloading calico to /opt/cni/bin
Adds new boolean configuration variable for calico network plugin
`ipip`. When it's enabled calico pool is created with '--ipip'
option (IP-over-IP encapsulation across hosts).
Also refactor pool creation tasks to simplify logic and make tasks
more readable.
