Add daily integration test of Packer example

[tpdownes]

This does a full run of our simple Packer example:

• provisions a new network and subnetwork with appropriate firewall rules
• builds and deletes a VM image

The main area of concern I have is that only 1 of these builds can be executed concurrently because the subnetwork name is static. The intent is to run this only as a daily trigger so I don't think this should be a blocker - eliminating the static nature of the subnetwork name is also planned. In the meantime, it will be a test of the ability of the VPC module to reliably cleanup after itself.

Submission Checklist

• Have you installed and run this change against pre-commit? pre-commit install
• Are all tests passing? make tests
• If applicable, have you written additional unit tests to cover this
  change?
• Is unit test coverage still above 80%?
• Have you updated any application documentation such as READMEs and user
  guides?
• Have you followed the guidelines in our Contributing document?

[nick-stroud]

LGTM. I know @cboneti had some interest in this pr. I will leave it up to you if you want him to take one last look.

[tpdownes]

@cboneti for clarity I'd like an approval since you raised some issues here and directly