[FLINK-24212][kerbernets] fix the problem that kerberos krb5.conf file is mounted as empty directory, not a expected file

[lzshlzsh]

What is the purpose of the change

If the user-provided krb5 conf file is not named krb5.conf (e.g named mykrb5.conf)，the mount path /etc/krb5.conf in pod will be an empty directory, not a file that we expect.

Brief change log

• KerberosMountDecorator#decorateFlinkPod

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: Kubernetes deployment
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not documented

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Automated Checks

Last check on commit 0cf21dd (Wed Sep 08 12:28:35 UTC 2021)

Warnings:

• No documentation files were touched! Remember to keep the Flink docs up to date!
• This pull request references an unassigned Jira ticket. According to the code contribution guide, tickets need to be assigned before starting with the implementation work.

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Review Progress

• ❓ 1. The [description] looks good.
• ❓ 2. There is [consensus] that the contribution should go into to Flink.
• ❓ 3. Needs [attention] from.
• ❓ 4. The change fits into the overall [architecture].
• ❓ 5. Overall code [quality] is good.

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CI report:

• 7140554 Azure: SUCCESS

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[KarmaGYZ]

Thanks for the contribution @lzshlzsh . Your fix looks good. Have you verified it in your local env? Also, it would be good to add a test for it.

[lzshlzsh]

Thanks for the contribution @lzshlzsh . Your fix looks good. Have you verified it in your local env? Also, it would be good to add a test for it.

Yes, I have verified it in my company production env.
Thanks for your advise, i will add a test for it,

[lzshlzsh]

Thanks for the contribution @lzshlzsh . Your fix looks good. Have you verified it in your local env? Also, it would be good to add a test for it.

@KarmaGYZ I have added a test for it. Could you help review the code ?

[KarmaGYZ]

Thanks for the update, @lzshlzsh . It LGTM except for some minor comments. Also, please squash your two commits and add the prefix "[FLINK-24212][k8s]" to your commit message.

[KarmaGYZ]

+1 to merge it once CI is green. @xintongsong Would you like to take another look and help to merge it?

[lzshlzsh]

@flinkbot run travis
@flinkbot run azure