Allow the use of existing VPCs

[tibers]

Is your feature request related to a problem? Please describe.
I'm always frustrated when [...] my rigid corporate environment has an existing VPC with security controls which they want me to use for hosting rancher.

Describe the solution you'd like
Please let me specify a VPC to install rancher into rather than creating a new VPC.

Describe alternatives you've considered
Jumping off a bridge. Becoming a chicken farmer. Going into politics.

Additional context

[arashkaffamanesh]

Is provided with Terraform Rancher Provider (for RKE) in 0.7.x release, Kubespray support will be deprecated and we're going to provide support for kubeadm with this repo, which supports existing VPCs or new VPCs:
https://github.com/scholzj/terraform-aws-kubernetes

[arashkaffamanesh]

It would be nice to have the REST API for TK8 Web.