Missing examples for curl in Cloud Files.

Before:

```
# ruby sample_completion.rb | grep cloud-files | grep shell
cloud-files          / change_object_metadata         / shell       : missing
cloud-files          / get_object_sdk                 / shell       : missing
cloud-files          / set_container_as_cdn           / shell       : missing
```

After:

```
# ruby sample_completion.rb | grep cloud-files | grep shell
```

I also merged `update_object_metadata` with `change_object_metadata` and used `change_object_metadata`, since the examples there more closely fit with the quickstart narrative.