BR: retry for PD request error and TiKV IO error (#27803)

[joccau]

What problem does this PR solve?

Cherry-pick for pr(pingcap/tidb#27803) to fix issue(pingcap/tidb#27787)

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test

Release note

Retry pd request and TiKV IO timeout error

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• YuJuncen
• kennytm

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[joccau]

/rebuild

[joccau]

/run-integration-test

[joccau]

./build

[joccau]

/build

[kennytm]

please fix gofmt.

[2021-09-08T03:11:33.854Z]  	"google.golang.org/grpc/credentials"

[2021-09-08T03:11:33.854Z]  	"google.golang.org/grpc/keepalive"

[2021-09-08T03:11:33.854Z]  

[2021-09-08T03:11:33.854Z] +	"google.golang.org/grpc/status"

[2021-09-08T03:11:33.854Z] +

[2021-09-08T03:11:33.854Z]  	berrors "github.com/pingcap/br/pkg/errors"

[2021-09-08T03:11:33.854Z]  	"github.com/pingcap/br/pkg/glue"

[2021-09-08T03:11:33.854Z]  	"github.com/pingcap/br/pkg/logutil"

[2021-09-08T03:11:33.854Z]  	"github.com/pingcap/br/pkg/pdutil"

[2021-09-08T03:11:33.854Z]  	"github.com/pingcap/br/pkg/utils"

[2021-09-08T03:11:33.854Z]  	"github.com/pingcap/br/pkg/version"

[2021-09-08T03:11:33.854Z] -	"google.golang.org/grpc/status"

[kennytm]

now it's the lints 😅

[2021-09-08T09:15:33.066Z]   ✘  https://revive.run/r#exported  exported function GetAllTiKVStoresWithRetry should have comment or be unexported  
[2021-09-08T09:15:33.066Z]   /home/jenkins/agent/workspace/br_ghpr_build/go/src/github.com/pingcap/br/pkg/conn/conn.go:109:1
[2021-09-08T09:15:33.066Z] 
[2021-09-08T09:15:33.067Z]   ✘  https://revive.run/r#exported  exported function NewImportSSTBackoffer should have comment or be unexported  
[2021-09-08T09:15:33.067Z]   /home/jenkins/agent/workspace/br_ghpr_build/go/src/github.com/pingcap/br/pkg/utils/backoff.go:47:1
[2021-09-08T09:15:33.067Z] 
[2021-09-08T09:15:33.067Z]   ✘  https://revive.run/r#exported  exported function NewDownloadSSTBackoffer should have comment or be unexported  
[2021-09-08T09:15:33.067Z]   /home/jenkins/agent/workspace/br_ghpr_build/go/src/github.com/pingcap/br/pkg/utils/backoff.go:51:1
[2021-09-08T09:15:33.067Z] 
[2021-09-08T09:15:33.067Z]   ✘  https://revive.run/r#exported  exported function NewPDReqBackoffer should have comment or be unexported  
[2021-09-08T09:15:33.067Z]   /home/jenkins/agent/workspace/br_ghpr_build/go/src/github.com/pingcap/br/pkg/utils/backoff.go:97:1

[kennytm]

rest LGTM

[YuJuncen]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 9b032f2

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #1436.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #1437.