Automatic merge from submit-queue
Extend secrets volumes with path control
As per [1] this PR extends secrets mapped into volume with:
* key-to-path mapping the same way as is for configmap. E.g.
```
{
"apiVersion": "v1",
"kind": "Pod",
"metadata": {
"name": "mypod",
"namespace": "default"
},
"spec": {
"containers": [{
"name": "mypod",
"image": "redis",
"volumeMounts": [{
"name": "foo",
"mountPath": "/etc/foo",
"readOnly": true
}]
}],
"volumes": [{
"name": "foo",
"secret": {
"secretName": "mysecret",
"items": [{
"key": "username",
"path": "my-username"
}]
}
}]
}
}
```
Here the ``spec.volumes[0].secret.items`` added changing original target ``/etc/foo/username`` to ``/etc/foo/my-username``.
* secondly, refactoring ``pkg/volumes/secrets/secrets.go`` volume plugin to use ``AtomicWritter`` to project a secret into file.
[1] https://github.com/kubernetes/kubernetes/blob/master/docs/design/configmap.md#changes-to-secret
eb733cbf45