Fix gcloud provider unit test to use fake instead of disk
Fix gcloud provider unit test to use fake instead of disk

ihmccreery/puppetlabs-gce_compute,icg-puppet/puppetlabs-gce_compute,hunner/puppetlabs-gce_compute,puppetlabs/puppetlabs-gce_compute,ihmccreery/puppetlabs-gce_compute,icg-puppet/puppetlabs-gce_compute,puppetlabs/puppetlabs-gce_compute,hunner/puppetlabs-gce_compute