Try both rpm and dpkg when searching for OS dep

This seems reasonably to me. Any reason why it could cause havoc?

We try `rpm` first. Some systems will have both `rpm` and `dpkg` installed but the os packages will only be installed with one of them.
On systems where `dpkg` is the go-to command for checking OS deps, but which have `rpm` also available, this will fail. The check will be run with `rpm`, setting `found` to `False`, and hence skipping the check with `dpkg`.

Why not simply chaing the `found is None` part to `not found`? That way, you'll check with `dpkg` as a fallback...