Retrieves a list GPUs you can attach to an instance
gce_list_gpus(filter = NULL, maxResults = NULL, pageToken = NULL,
  project = gce_get_global_project(), zone = gce_get_global_zone())Sets a filter expression for filtering listed resources, in the form filter=expression
The maximum number of results per page that should be returned
Specifies a page token to use
Project ID for this request
The name of the zone for this request
To filter you need a single string in the form field_name eq|ne string 
  e.g. gce_list_instances("status eq RUNNING") where eq is 'equals' and ne is 'not-equals'.
Other GPU instances: gce_check_gpu,
  gce_vm_gpu