Bugfix: Destroying a non existent server array should return False.

There were two bugs here...

1. Logging string problem (unmatched %s).
2. The Destroy actor needs to pay attention to whether the Terminate
actor succeeded. If it does not, it should raise an exception and get
out of there.
If I return `false` here, then I have to catch the `false` inside the `_execute()` and return it. This was simpler IMO.