Move parameter list to top
Move parameter list to top

to make the gce_instance provider more consistent
with other providers.
puppetlabs/puppetlabs-gce_compute,puppetlabs/puppetlabs-gce_compute,ihmccreery/puppetlabs-gce_compute,icg-puppet/puppetlabs-gce_compute,GoogleCloudPlatform/puppetlabs-gce_compute,GoogleCloudPlatform/puppetlabs-gce_compute,hunner/puppetlabs-gce_compute,hunner/puppetlabs-gce_compute,icg-puppet/puppetlabs-gce_compute,ihmccreery/puppetlabs-gce_compute