Create a build capability for VM factory

In simplifying the initial vm-factory we removed build capabilities using packer. Builds are valuable performance improvement in the face of repeated deploys and alternate deploy environments. We'd like to bring that capability back into the project.

Some of the build variables removed include:

  PKR_VAR_flavor: "m1.medium-ruffner"
  PKR_VAR_source_image: "CentOS-7-x86_64-GenericCloud-2009"
  PKR_VAR_floating_ip_network: "uab-campus"
  PKR_VAR_security_groups: '["allow-ssh"]'
  PKR_VAR_skip_create_image: "false"
  PKR_VAR_ssh_username: "centos"
  PKR_VAR_networks: '["8cf2f12e-905d-46d9-bc70-b0897c65f75a"]'

We should likely rename these as VMF_BUILD_... and then map them to build-specific tooling vars like PKR_VAR_flavor at some internal tool selection point.