Build sacrificial VM image with Packer

[paseaf]

This PR should close #6
Refer to /packer/README.md for details

[paseaf]

Task notes

• Create a script to automate Terraform & Packer build
  Do it later when have time.
• Adapt Terraform to use Packer image
• update system packages and install Docker for Packer image
  Note: use update.sh to achieve unattended update.
• fix packer build error

  ubuntu-2204-with-docker.googlecompute.ubuntu-2204: Error waiting for SSH: Packer experienced an authentication error when trying to connect via SSH. This can happen if your username/password are wrong. You may want to double-check your credentials as part of your debugging process. original error: ssh: handshake failed: ssh: unable to authenticate, attempted methods [none publickey], no supported methods remain
  Solution: Follow Packer - Running outside of Google Cloud to set up GOOGLE_APPLICATION_CRENDENTIALS env variable.

• packer build seems to already starts a new vm instance?
  No. It just creates a vm and use it to create the image. The VM is deleted once the image is created.
• Does machine type matter in Packer setup?
  Not sure. Check it out when have to.

Takeaways

• Packer prints script commands in red!
  
  Answer: It's an expected behavior caused by set -x!! See here
• Bug: packer build fails randomly with Could not get lock /var/lib/apt/lists/lock. It is held by process 1712 (apt-get)
  Solution:
  Wait for locked file with modified apt-get:

  #  https://github.com/geerlingguy/packer-boxes/issues/7#issuecomment-425641793
  function apt-get() {
    while fuser -s /var/lib/apt/lists/lock;
    do echo 'apt-get is waiting for the lock release ...';
      sleep 1;
    done;
    /usr/bin/apt-get "$@";
  }

• How to create meaningful image names automatically with packer?
  Use HCL Functions!! ({{timestamp}})
  example: https://github.com/vancluever/packer-terraform-example/blob/master/packer/ami.json
  For simplicity: use the same image name, and overwrite old once when build again!

[paseaf]

LGTM!