Exit MonitorEvaluation once stream is closed

As we pass the context to the Nomad API event stream, they close
the event stream once the passed context is cancelled. We use this
to exit our receive loop on the event stream once the stream is closed,
instead of having to check the context manually.

nomad/nomad.go

@@ -66,17 +66,12 @@ func (a *ApiClient) LoadRunners(jobId string) (runnerIds []string, err error) {
 }
 
 func (a *ApiClient) MonitorEvaluation(evalID string, ctx context.Context) error {
-	var events *nomadApi.Events
 	stream, err := a.EvaluationStream(evalID, ctx)
 	if err != nil {
 		return err
 	}
-	for {
-		select {
-		case events = <-stream:
-		case <-ctx.Done():
-			return nil
-		}
+	// If ctx is cancelled, the stream will be closed by Nomad and we exit the for loop.
+	for events := range stream {
 		if events.IsHeartbeat() {
 			continue
 		}
@@ -97,6 +92,7 @@ func (a *ApiClient) MonitorEvaluation(evalID string, ctx context.Context) error
 			}
 		}
 	}
+	return nil
 }
 
 // checkEvaluation checks whether the given evaluation failed.