fix pointer type of macro used to convert rs string to c string
fix pointer type of macro used to convert rs string to c string

In this commit we also add todo and warning to avoid using them +
remove them in future.

Signed-off-by: Sahid Orentino Ferdjaoui <f799991784850b8d4b84e1fdbe797720df9aae1a@canonical.com>

sahid/libvirt-rs