rest-server api: submit(create) a job should return the created job

[hao1939]

As restful verbs defined, rest-server should better return the created object for a 'create/update' operation.

Now the submit job api POST /api/v1/user/:username/jobs returns:

{
  "message": "update job $jobName successfully"
}

[scarlett2018]

As restful verbs defined, rest-server should better return the created object for a 'create/update' operation.

Now the submit job api POST /api/v1/user/:username/jobs returns:

{
  "message": "update job $jobName successfully"
}

Combine with #2315 which is planned in 0.12.0