test(dm): fix using pgrep to check argument pattern (#6572)

[ti-chi-bot]

This is an automated cherry-pick of #6572

Signed-off-by: lance6716 lance6716@gmail.com

What problem does this PR solve?

Issue Number: close #6526, close #5731, close #5287

What is changed and how it works?

• we use kill_process dm-worker1 in test script, and finally it will become pgrep dm-worker1. This is not right because dm-worker1 is in arguments and pgrep only check process name.
• old problems, same root cause but different case as flaking test ALTER TABLE shardddl.tb ADD COLUMN new_col1 INT DEFAULT -1 #5807
• after syncer processes RowsEvent, check_sync_diff will pass, but XIDEvent may have not been written to relay log. We retry checking for 5 seconds.

Check List

Tests

• Integration test
• Manual test (add detailed scripts or steps below)

# lance @ lance6716-nuc10i7fnh in ~/go/src/github.com/pingcap/tiflow on git:master o [14:31:49] 
$ pgrep -f dm-worker1     
467807

# lance @ lance6716-nuc10i7fnh in ~/go/src/github.com/pingcap/tiflow on git:master x [14:32:09] 
$ pgrep dm-worker1                                       

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

 `None`.

[ti-chi-bot]

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[ti-chi-bot]

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