cloudfoundry-incubator/fissile: docker/docker.go; 20 LoC

Found a possible issue in [cloudfoundry-incubator/fissile](https://www.github.com/cloudfoundry-incubator/fissile) at [docker/docker.go](https://github.com/cloudfoundry-incubator/fissile/blob/b8e8e6af42ef32efc5387f6a69312feacc78e96c/docker/docker.go#L593-L612)

Below is the message reported by the analyzer for this snippet of code. Beware that the analyzer only reports the first
issue it finds, so please do not limit your consideration to the contents of the below message.

> range-loop variable src used in defer or goroutine at line 598

[Click here to see the code in its original context.](https://github.com/cloudfoundry-incubator/fissile/blob/b8e8e6af42ef32efc5387f6a69312feacc78e96c/docker/docker.go#L593-L612)

Click here to show the 20 line(s) of Go which triggered the analyzer.

```go
for src, dest := range opts.StreamIn {
tarStream := tarstream.New(fsWithSymlinks)
r, w := io.Pipe()

go func() {
tarErr := tarStream.CreateTarStream(src, false, w)
if tarErr != nil {
w.CloseWithError(tarErr)
}
w.Close()
}()

err = d.client.UploadToContainer(container.ID, dockerclient.UploadToContainerOptions{
InputStream: r,
Path: dest,
})
if err != nil {
return -1, container, fmt.Errorf("Error running in container: %s. Error streaming data into container: %s", container.ID, err)
}
}

```

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See the descriptions of the classifications [here](https://github.com/github-vet/rangeclosure-findings#how-can-i-help) for more information.

commit ID: b8e8e6af42ef32efc5387f6a69312feacc78e96c