(CISC-973) Handle vars in gcp provisioner

[HelenCampbell]

This work is to allow the addiiton of 'vars' into the inventory file for gcp provisioning, as required by comply. Tested against https://github.com/puppetlabs/comply/runs/1656251077?check_suite_focus=true with the following result:

Run cat ./inventory.yaml

---
version: 2
groups:
- name: docker_nodes
  targets: []
- name: ssh_nodes
  targets:
  - uri: 104.155.47.124
    config:
      transport: ssh
      ssh:
        user: litmuskww5w1fm
        password: ******************
        host-key-check: false
        port: 22
        run-as: root
    facts:
      provisioner: provision::provision_service
      platform: centos-7
      uuid: 197d8ae6-027f-4b5f-b4c9-1509dffd0e5a
    vars:
      role: pe
  - uri: 34.76.79.34
    config:
      transport: ssh
      ssh:
        user: litmusiyvs9lpg
        password: ****************
        host-key-check: false
        port: 22
        run-as: root
    facts:
      provisioner: provision::provision_service
      platform: centos-7
      uuid: 6a4f6c84-d33a-4e71-98b2-fe945776e24b
    vars:
      role: comply