fixed Unknown nodes from being incorrectly reported as OutOfService

Hi,

We noticed that nodes with a `Unknown` status were incorrectly being reported as `OutOfService`:

```bash
CheckELBNodes WARNING: InService: 2 (i-a660d3e5, i-2aef7868); OutOfService: 0 (i-a775c5e7)
```

This change fixes that and should output the following instead:

```bash
CheckELBNodes WARNING: InService: 2 (i-a660d3e5, i-2aef7868); OutOfService: 0; Unknown: 1 (i-a775c5e7)
```

This will help us in differentiating between `Unknown` and `OutOfService` nodes and allow us to investigate further.