Cloud4upgrade

Implementation of a upgrade subcommand to upgrade an existing cloud to the next version. Based on the work of @rhafer, with contributions of @freyes and @nkrinner
Something like this?

```
if iscloudver 3; then
    update_version=4
    touch ~/update-to-4
elif iscloudver 4; then
    update_version=5
    touch ~/update-to-5
else
    echo "Update target does not yet exist"
    exit 1
fi
```