backup: fix issue 1657 (#2071)

[sre-bot]

cherry-pick #2071 to release-1.1

---

What problem does this PR solve?

fixes #1657

What is changed and how does it work?

create a stdout pipe from the exec process, and read the pipe message in a for loop, If the output meesage with ERROR, add to the backup status message information

Check List

Tests

• Manual test (add detailed scripts or steps below)
  It seems the log will output intime and the backup status messsage is

  status:
    backupPath: ""
    backupSize: 0
    commitTs: ""
    conditions:
    - lastTransitionTime: "2020-03-30T12:14:02Z"
      message: ""
      reason: ""
      status: "True"
      type: Scheduled
    - lastTransitionTime: "2020-03-30T12:14:03Z"
      message: ""
      reason: ""
      status: "True"
      type: Running
    - lastTransitionTime: "2020-03-30T12:14:36Z"
      message: "cluster cluster/sa-backup-s3, wait pipe message failed, errMsg [2020/03/30
        12:14:36.196 +00:00] [ERROR] [push.go:106] [\"backup occur unknown error\"]
        [error=\"Io(Custom { kind: Other, error: \\\"failed to put object Couldn\\\\'t
        find AWS credentials in environment, credentials file, or IAM role.\\\" })\"]
        [stack=\"github.com/pingcap/log.Error\\n\\t/go/pkg/mod/github.com/pingcap/log@v0.0.0-20200117041106-d28c14d3b1cd/global.go:42\\ngithub.com/pingcap/br/pkg/backup.(*pushDown).pushBackup\\n\\t/home/jenkins/agent/workspace/build_br_master/go/src/github.com/pingcap/br/pkg/backup/push.go:106\\ngithub.com/pingcap/br/pkg/backup.(*Client).backupRange\\n\\t/home/jenkins/agent/workspace/build_br_master/go/src/github.com/pingcap/br/pkg/backup/client.go:404\\ngithub.com/pingcap/br/pkg/backup.(*Client).BackupRanges.func2\\n\\t/home/jenkins/agent/workspace/build_br_master/go/src/github.com/pingcap/br/pkg/backup/client.go:316\"]\n\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0,
        err: exit status 1"
      reason: BackupDataToRemoteFailed
      status: "True"
      type: Failed
    timeCompleted: null
    timeStarted: null

Code changes

• Has Go code change

[DanielZhangQD]

LGTM

[DanielZhangQD]

/merge

[sre-bot]

Your auto merge job has been accepted, waiting for 2068

[sre-bot]

/run-all-tests

[sre-bot]

/run-all-tests