Makes disk delete optionally async

lib/fog/google/models/compute/disk.rb

@@ -42,14 +42,16 @@ module Fog
           service.disks.merge_attributes(data)
         end
 
-        def destroy
+        def destroy(async=true)
           requires :name, :zone_name
           operation = service.delete_disk(name, zone_name)
           # wait until "DONE" to ensure the operation doesn't fail, raises exception on error
+          if not async
             Fog.wait_for do
               operation = service.get_zone_operation(zone_name, operation.body["name"])
               operation.body["status"] == "DONE"
             end
+          end
           operation
         end