CreateCluster TODO(peter): document opts is a slice of all node VM specs to be provisioned for the cluster.

DestroyCluster TODO(peter): document.

ExtendCluster TODO(peter): document.

GCAWS garbage collects expired clusters, unused SSH keys for a single or multiple AWS accounts.

GCAzure iterates through subscription IDs passed in --azure-subscription-names and performs GC on them.

GCClusters checks all cluster to see if they should be deleted.

GCDNS deletes dangling DNS records for clusters that have been destroyed.

GrowCluster adds new nodes to an existing cluster.

ListCloud returns information about all instances (across all available providers).

ShrinkCluster removes tail nodes from an existing cluster.

Cloud contains information about all known clusters (across multiple cloud providers).

A Cluster is created by querying various vm.Provider instances.

Clusters contains a set of clusters (potentially across multiple providers), keyed by the cluster name.