update log4j2 to 2.17.1

[FrankChen021]

Fixes the latest vulnerability (44832) which also affects its prior release 2.17.0 that is being use by Druid on master branch.

This vulnerability allows RCE for attackers by constructing malicious code for log4j JDBC appender. Druid's default configuration does not use this kind of appender, is not affected.

Description

https://logging.apache.org/log4j/2.x/security.html#CVE-2021-44832

This PR has:

• been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• added documentation for new or modified features or behaviors.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added or updated version, license, or notice information in licenses.yaml
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• added integration tests.
• been tested in a test Druid cluster.

[FrankChen021]

This is the 4th update since the first CVE announced earlier in this month. To be honest, I'm tired of such thing. Hope there won't be any vulnerability in log4j in the upcoming new year which will give all of us a relief.

[gianm]

LGTM, thanks!