task_checker: don't resume for binlog not found (#1210)

[ti-srebot]

cherry-pick #1210 to release-2.0

---

What problem does this PR solve?

[2020/10/23 02:03:41.082 +00:00] [ERROR] [subtask.go:295] ["unit process error"] [subtask=test-all] [unit=Sync] ["error information"="{\"ErrCode\":50000,\"ErrClass\":\"not-set\",\"ErrScope\":\"not-set\",\"ErrLevel\":\"high\",\"Message\":\"ERROR 1236 (HY000): Could not find first log file name in binary log index file\"}"]
[2020/10/23 02:03:45.882 +00:00] [WARN] [task_checker.go:315] ["backoff skip auto resume task"] [component="task checker"] [task=test-all] [latestResumeTime=2020/10/23 02:03:40.882 +00:00] [duration=5m0s]

What is changed and how it works?

don't resume it

Check List

Tests

• Unit test

Code changes

Side effects

Related changes

• Need to cherry-pick to the release branch
• Need to be included in the release note

[csuzhangxc]

LGTM