Add external IP output to vm-instance module

[tpdownes]

• if public IPs are enabled (default), the output is the list of external "NAT" IPs for each VM
• if public IPs are disabled explicitly, the output is the empty list

We already have a task to expand test coverage of this module and I will add public/private IP to its description.

A blueprint that one can use to test this is below. The terraform outputs will yield:

external_ip_private = []
external_ip_public = [
  "104.197.82.46",
  "35.223.38.149",
  "34.71.34.33",
  "34.72.25.136",
  "34.123.15.216",
]
internal_ip_private = [
  "10.0.0.9",
  "10.0.0.3",
  "10.0.0.8",
]
internal_ip_public = [
  "10.0.0.2",
  "10.0.0.4",
  "10.0.0.7",
  "10.0.0.5",
  "10.0.0.6",
]

---
blueprint_name: vm-test

vars:
  project_id:  ## Set GCP Project ID Here ##
  deployment_name: vm-test-001
  region: us-central1
  zone: us-central1-c


deployment_groups:
- group: vm_test
  modules:
  - source: modules/network/vpc
    kind: terraform
    id: network1
  - source: modules/compute/vm-instance
    kind: terraform
    id: private
    use:
    - network1
    settings:
      instance_count: 3
      name_prefix: private
      disable_public_ips: true
    outputs:
    - external_ip
    - internal_ip
  - source: modules/compute/vm-instance
    kind: terraform
    id: public
    use:
    - network1
    settings:
      instance_count: 5
      name_prefix: public
    outputs:
    - external_ip
    - internal_ip

Submission Checklist

• Have you installed and run this change against pre-commit? (pre-commit install)
• Are all tests passing? (make tests)
• Have you written unit tests to cover this change?
• Is unit test coverage still above 80%?
• Have you updated all applicable documentation?
• Have you followed the guidelines in our Contributing document?

[heyealex]

LGTM
Only comment I considered adding was updating this and internal_ip to be plural since they output lists. That should probably be done separately though.

[tpdownes]

Yeah, I have a task that describes the plural/singular issue but consider that a specific change with potential breaking implications.