When Op Type is not registered, log the hostname of the machine that

it is running on in the error message, since the message could be routed
back during a failure on a remote binary, and it is hard to tell which
machine it came from.

Ideally, we'd somehow log the name of the binary running instead, but
we don't have a function to get that right now.

PiperOrigin-RevId: 156337679