An Environment cannot have a VPC specified without specifying a Cluster

[SamStephens]

When defining an Environment, either you specify neither a VPC and Cluster, and the Environment creates its own VPC and Cluster, or you provide both.

However, I (and I suspect others) have an existing VPC I want my Environment to live within, but I'd still like to have my Environment do the heavy lifting of actually defining the Cluster etc.