Fix flake on failed podman-remote build

We have a race condition where podman build can fail
but still return an exit code of 0.  This PR ensures
that as soon as the build fails, the failed flag is set
eliminating the race.

Fixes: https://github.com/containers/podman/issues/10029

[NO TESTS NEEDED] Tests of failed builds are already in place, and
the elimination of the race should be enough.

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

pkg/api/handlers/compat/images_build.go

@@ -462,12 +462,17 @@ func BuildImage(w http.ResponseWriter, r *http.Request) {
 		buildOptions.Timestamp = &ts
 	}
 
+	var (
+		imageID string
+		failed  bool
+	)
+
 	runCtx, cancel := context.WithCancel(context.Background())
-	var imageID string
 	go func() {
 		defer cancel()
 		imageID, _, err = runtime.Build(r.Context(), buildOptions, query.Dockerfile)
 		if err != nil {
+			failed = true
 			stderr.Write([]byte(err.Error() + "\n"))
 		}
 	}()
@@ -483,8 +488,6 @@ func BuildImage(w http.ResponseWriter, r *http.Request) {
 	w.Header().Add("Content-Type", "application/json")
 	flush()
 
-	var failed bool
-
 	body := w.(io.Writer)
 	if logrus.IsLevelEnabled(logrus.DebugLevel) {
 		if v, found := os.LookupEnv("PODMAN_RETAIN_BUILD_ARTIFACT"); found {
@@ -525,7 +528,6 @@ loop:
 			}
 			flush()
 		case e := <-stderr.Chan():
-			failed = true
 			m.Error = string(e)
 			if err := enc.Encode(m); err != nil {
 				logrus.Warnf("Failed to json encode error %v", err)