Unacceptable errors should be handled instead of directly `log.Fatal()`

[JQWong7]

Feature Request

Is your feature request related to a problem? Please describe:

user will get confuse since exit suddently.
such as:

tidb-tools/sync_diff_inspector/diff.go

Lines 561 to 566 in 1cf55fb

	if count1+count2 != count {
	log.Fatal("the count is not correct",
	zap.Int64("count1", count1),
	zap.Int64("count2", count2),
	zap.Int64("count", count))
	}

Describe the feature you'd like:

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy:

[alastori]

I think feature requests should now go to the pingcap/tiflow repo: https://github.com/pingcap/tiflow/tree/master/sync_diff_inspector