Move conflict messaged to Debug Logging (googleforgames#1232)

Conflicts when attempting to update Kubernetes resources is expected and
will happen frequently in Agones.

Currently they are reported as errors, and (a) produce a lot of noise,
and (b) are reported as errors, which can often be seen as potential
issues by end users, as well as red-herring reasons for actual issues.

We may want to wait until googleforgames#1220 is complete before merging.

Will help with issues also raised in googleforgames#1218.

pkg/util/workerqueue/workerqueue.go

@@ -26,6 +26,7 @@ import (
 	"agones.dev/agones/pkg/util/runtime"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
+	k8serror "k8s.io/apimachinery/pkg/api/errors"
 	"k8s.io/apimachinery/pkg/util/wait"
 	"k8s.io/client-go/tools/cache"
 	"k8s.io/client-go/util/workqueue"
@@ -150,8 +151,14 @@ func (wq *WorkerQueue) processNextWorkItem() bool {
 	}
 
 	if err := wq.SyncHandler(key); err != nil {
+		// Conflicts are expected, so only show them in debug operations.
+		if k8serror.IsConflict(err) {
+			wq.logger.WithField(wq.keyName, obj).Debug(err)
+		} else {
+			runtime.HandleError(wq.logger.WithField(wq.keyName, obj), err)
+		}
+
 		// we don't forget here, because we want this to be retried via the queue
-		runtime.HandleError(wq.logger.WithField(wq.keyName, obj), err)
 		wq.queue.AddRateLimited(obj)
 		return true
 	}