Experimental installation of addon components via kpt

[bboreham]

I created a profiles package structured a bit like addons, that uses the kpt command to fetch and manipulate manifests.

(kpt must be already on your path for this to work)

As a demonstration, re-do the Weave Net installation and CIDR setting using kpt.

A PR to add the Kptfile for parameter setting is at weaveworks/weave#3853

[bboreham]

Further musing:

• We could remove the weave-net.yaml currently baked into the wksctl binary, or we could re-instate it as an option to avoid needing to fetch files from github.

• I expected to be able to remove SetWeaveNetPodCIDRBlock(), but it is still called from wksctl init. This command needs updating to fit with current code, but given a more flexible templating system should perhaps not exist at all.