For example, we create a workspace at [0], then write directly into it at [1]. Using that workspace allows us to be confident we aren't leaking any files  when we clean up [2]. With this change, there will be a write outside of the virtual "workspace" we've set up and we can't guarantee that everything gets cleaned up.

[0] https://github.com/coreos/coreos-cloudinit/blob/master/system/file_test.go#L12
[1] https://github.com/coreos/coreos-cloudinit/blob/master/system/file_test.go#L21
[2] https://github.com/coreos/coreos-cloudinit/blob/master/system/file_test.go#L16