Add a new command for generating example TFjobs (#509)

This command adds a new command genjob to hack/ directory. The command
generates TFJobs for testing purpose. Currently the generated jobs are
following the definitions of examples/tf_job.yaml and
examples/tf_job_gpu.yaml.

Example usage:
```
$ ./genjob --kube-config-path ~/.kube/config --nr-tfjobs 30 --use-gpu --scheduler-name tfjob
```

hack/genjob/genjob.go

@@ -0,0 +1,120 @@
+// Copyright 2018 The Kubeflow Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//       http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"time"
+
+	v1alpha1 "github.com/kubeflow/tf-operator/pkg/apis/tensorflow/v1alpha1"
+	tfjobclient "github.com/kubeflow/tf-operator/pkg/client/clientset/versioned"
+	v1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/client-go/tools/clientcmd"
+)
+
+type opts struct {
+	kubeConfigPath string
+	useGPU         bool
+	nrTFJobs       uint
+	namespace      string
+	schedulerName  string
+}
+
+func (o *opts) addFlags(fs *flag.FlagSet) {
+	fs.StringVar(&o.kubeConfigPath, "kube-config-path", "", "a path of k8s config")
+	fs.UintVar(&o.nrTFJobs, "nr-tfjobs", 1, "a number of generated TFJobs")
+	fs.BoolVar(&o.useGPU, "use-gpu", false, "generate TFJob which uses GPU")
+	fs.StringVar(&o.namespace, "namespace", "default", "namespace of k8s")
+	fs.StringVar(&o.schedulerName, "scheduler-name", "default", "scheduler name of k8s")
+}
+
+func tfjobTemplate(jobName string, gpu bool, schedulerName string) *v1alpha1.TFJob {
+	one := int32(1)
+	job := &v1alpha1.TFJob{
+		TypeMeta: metav1.TypeMeta{
+			APIVersion: "kubeflow.org/v1alpha1",
+			Kind:       "TFJob",
+		},
+		ObjectMeta: metav1.ObjectMeta{
+			Name: jobName,
+		},
+		Spec: v1alpha1.TFJobSpec{
+			SchedulerName: schedulerName,
+			ReplicaSpecs: []*v1alpha1.TFReplicaSpec{
+				{
+					Replicas: &one,
+					Template: &v1.PodTemplateSpec{
+						Spec: v1.PodSpec{
+							Containers: []v1.Container{
+								{
+									Name: "tensorflow",
+								},
+							},
+							RestartPolicy: v1.RestartPolicyOnFailure,
+						},
+					},
+				},
+			},
+		},
+	}
+
+	if !gpu {
+		job.Spec.ReplicaSpecs[0].TFReplicaType = v1alpha1.WORKER
+		job.Spec.ReplicaSpecs[0].Template.Spec.Containers[0].Image = "gcr.io/tf-on-k8s-dogfood/tf_sample:dc944ff"
+	} else {
+		job.Spec.ReplicaSpecs[0].TFReplicaType = v1alpha1.MASTER
+		job.Spec.ReplicaSpecs[0].Template.Spec.Containers[0].Image = "gcr.io/tf-on-k8s-dogfood/tf_sample_gpu:dc944ff"
+		job.Spec.TerminationPolicy = &v1alpha1.TerminationPolicySpec{
+			Chief: &v1alpha1.ChiefSpec{
+				ReplicaName: string(v1alpha1.MASTER),
+			},
+		}
+	}
+
+	return job
+}
+
+func main() {
+	o := &opts{}
+	o.addFlags(flag.CommandLine)
+	flag.Parse()
+
+	config, err := clientcmd.BuildConfigFromFlags("", o.kubeConfigPath)
+	if err != nil {
+		fmt.Printf("failed to build config with kubeconfig %s: %v\n", o.kubeConfigPath, err)
+		os.Exit(1)
+	}
+
+	tfJobClient, err := tfjobclient.NewForConfig(config)
+	if err != nil {
+		fmt.Printf("failed to create a tfjobclient %v", err)
+		os.Exit(1)
+	}
+
+	timestamp := time.Now().Nanosecond()
+
+	for i := uint(0); i < o.nrTFJobs; i++ {
+		jobName := fmt.Sprintf("tfjob-%d-%d", timestamp, i)
+		job := tfjobTemplate(jobName, o.useGPU, o.schedulerName)
+		_, err := tfJobClient.KubeflowV1alpha1().TFJobs(o.namespace).Create(job)
+		if err != nil {
+			fmt.Printf("failed to create TFJob %s: %v\n", job.ObjectMeta.Name, err)
+			os.Exit(1)
+		}
+	}
+}