add bestTrialId to statusJob status

[hougangliu]

Fixes: #305

---

This change is 

[hougangliu]

/assign @richardsliu @YujiOshima

Only pkg/api/api.proto is updated and changes of other files under pkg/api/ are automatically generated.

[hougangliu]

After a studyJob completed, user can get bestTrialId in studyjob status, then he can call GetTrial gRpc to get hyperparameter detail.

apiVersion: kubeflow.org/v1alpha1
kind: StudyJob
metadata:
  ...
  name: random-example
  namespace: kubeflow 
  resourceVersion: "88427"
spec:
  metricsnames:
  - accuracy
  objectivevaluename: Validation-accuracy
  optimizationgoal: 0.99
  optimizationtype: maximize
  owner: crd
  parameterconfigs:
  - feasible:
      max: "0.03"
      min: "0.01"
    name: --lr
    parametertype: double
  - feasible:
      max: "5"
      min: "2"
    name: --num-layers
    parametertype: int
  - feasible:
      list:
      - sgd
      - adam
      - ftrl
    name: --optimizer
    parametertype: categorical
  requestcount: 1
  studyName: random-example
  suggestionSpec:
    requestNumber: 3
    suggestionAlgorithm: random
    suggestionParameters:
    - name: SuggestionCount
      value: "0"
  workerSpec:
    goTemplate:
      rawTemplate: |-
        apiVersion: batch/v1
        kind: Job
        metadata:
          name: {{.WorkerID}}
          namespace: kubeflow
        spec:
          template:
            spec:
              containers:
              - name: {{.WorkerID}}
                image: katib/mxnet-mnist-example
                command:
                - "python"
                - "/mxnet/example/image-classification/train_mnist.py"
                - "--batch-size=64"
                {{- with .HyperParameters}}
                {{- range .}}
                - "{{.Name}}={{.Value}}"
                {{- end}}
                {{- end}}
              restartPolicy: Never
status:
  bestObjectiveValue: 0.980792
  bestTrialId: t0ce0e11284b4b73
  completionTime: 2018-12-24T07:37:15Z
  conditon: Completed
  earlyStoppingParameterId: ""
  lastReconcileTime: 2018-12-24T07:37:15Z
  startTime: 2018-12-24T07:31:17Z
  studyid: y33b9b01aa7bfcc3
  suggestionCount: 1
  suggestionParameterId: vb1d0a73fdfabe2f
  trials:
  - trialid: qae2e83646d61786
    workeridlist:
    - completionTime: 2018-12-24T07:37:14Z
      conditon: Completed
      kind: Job
      objectiveValue: 0.978205
      startTime: 2018-12-24T07:31:17Z
      workerid: p17f9325c8b65f68
  - trialid: jbd34ca57e76036b
    workeridlist:
    - completionTime: 2018-12-24T07:37:14Z
      conditon: Completed
      kind: Job
      objectiveValue: 0.97492
      startTime: 2018-12-24T07:31:17Z
      workerid: y5fd2ce56c1c5074
  - trialid: t0ce0e11284b4b73
    workeridlist:
    - completionTime: 2018-12-24T07:35:13Z
      conditon: Completed
      kind: Job
      objectiveValue: 0.980792
      startTime: 2018-12-24T07:31:17Z
      workerid: h8acd2157fd748ae

[hougangliu]

/retest

[YujiOshima]

@hougangliu Thanks! This is great! Please generate mocks by mockgen script

[YujiOshima]

@hougangliu It is better to have not only the best trialID but the best workerID.

[hougangliu]

@YujiOshima thanks! I will re-submit another patch to fix your comment after #303 merged

[hougangliu]

/retest

[richardsliu]

This request may be confusing with GetTrialsRequest above, since the names differ only by 1 letter and the parameters are the same. Maybe we should rename GetTrialsRequest to ListStudyTrialsRequest? @YujiOshima What do you think?

[hougangliu]

Ok, I can change it in another PR.
BTW, should we keep backward compatibility about GetTrialsRequest

[richardsliu]

Perhaps we should reconsider this when we define our Beta APIs. For now this looks good.

[richardsliu]

/lgtm
/approve

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