Bugfix: Destroying a non-existant 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 fails, then we immediately fail the Destroy actor
too.
Merge pull request #118 from Nextdoor/fix_destroy_actor

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