test: fix unstable wait rpc alive (#2095)

[ti-chi-bot]

This is an automated cherry-pick of #2095

What problem does this PR solve?

part of #2073

https://ci.pingcap.net/blue/organizations/jenkins/dm_ghpr_new_test/detail/dm_ghpr_new_test/2218/pipeline/ :

• waiting MySQL2 starting cost 32 * 2s
• some DM-master printed init nowand dm-master startup ... to stdout
• some DM-master printed init now to stdout

and https://ci.pingcap.net/blue/organizations/jenkins/dm_ghpr_new_test/detail/dm_ghpr_new_test/2143/pipeline/ :

• DM-master print nothing

What is changed and how it works?

increase retry from 10 times to 20 times 😂

Check List

Tests

• No code

Related changes

• Need to cherry-pick to the release branch

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Ehco1996
• glorv

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[Ehco1996]

/run-unit-tests

[glorv]

/merge

[ti-chi-bot]

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

Commit hash: 9eb8cfc