Userdata file created by module may not be fully written before executed

[jahkeup]

It seems that the code writing the userdata script to disk isn't ensuring the file is fully written when the module goes to execute the script.

https://github.com/aws/ec2-macos-init/blob/856afa4039a4acc4b4b87ef1c4595c59965f699a/lib/ec2macosinit/userdata.go#L45-L62

The defer file.Close() is the most suspicious here.