It's confusing to have both ACK vs. NACK and exit codes in an IPC reply - it opens up some weird situations where you can get a NACK with an OK, or an ACK with an error code. It also makes it difficult for the client to decide what to do with the reply. Right now, based, execd, and fenced send a NACK but no client actually does anything with that information.

Instead, let's get rid of the NACKs entirely and have clients just decide what to do based on the exit code. Once that's done, we can get rid of the tag argument to pcmk__ipc_send_ack.