Establish a stronger link between Machine and Cluster.

[dgoodwin]

On Feb 14 Cluster API working group call, a couple parties indicated we would like to make use of the ability to have multiple clusters to exist in one namespace, which would free up namespaces to be used for other levels of organization. (one customer, one cloud provider account, etc) In this case we would not be able to assume all machines or machine sets in a namespace belong to the single cluster in the namespace, and as such a stronger link between the two could be useful for some adopters of the cluster API.

[dgoodwin]

FWIW, in our very young OpenShift Cluster Operator code we've been using owner references to do this. (machine to machine set to cluster)

[rsdcastro]

This issue was moved to kubernetes-sigs/cluster-api#41