def start_extension_upgrade(resource_group_name, vm_scale_set_name, custom_headers:nil)
      response = start_extension_upgrade_async(resource_group_name, vm_scale_set_name, custom_headers:custom_headers).value!
      nil
    end
def start_extension_upgrade(resource_group_name, vm_scale_set_name, custom_headers:nil)
      response = start_extension_upgrade_async(resource_group_name, vm_scale_set_name, custom_headers:custom_headers).value!
      nil
    end
Starts a rolling upgrade to move all extensions for all virtual machine scale
 set instances to the latest available extension version. Instances which are
 already running the latest extension versions are not affected.

 @param resource_group_name [String] The name of the resource group.
 @param vm_scale_set_name [String] The name of the VM scale set.
 @param custom_headers [Hash{String => String}] A hash of custom headers that
 will be added to the HTTP request.