func RetriableErrorf(format string, a ...interface{}) error {
	return RetriableError{error: fmt.Errorf(format, a...)}
}
RetriableErrorf wraps a formatted error into a RetriableError.
package backoff
import (
	"context"
	"errors"
	"fmt"
	"math/rand"
	"time"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/status"
)
type RetriableError struct {
	error
}