rax module: Return untouhced servers with exact_count

This pull request addresses #6778

With this pull request existing servers that are untouched by the un will be returned in the response from the module.

As describe in a comment on the other ticket:

`instances` will only contain servers that are:

1. successfully created during the run
1. servers matching the group
1. servers that were not just deleted

So when servers are deleted, they will not show up in `instances`, they will only be available via `success`, `timeout` or `error` in such a case.

There is also a slight behavior change with `create`, in that it will not include servers who entered an error state or timed out while waiting. instances in this case will only include already created matching servers and servers just created successfully.