Fix missing attributes in RedisCluster spans

[a-cid]

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Description

Modifies _set_connection_attributes to handle conn being an instance of redis.cluster.RedisCluster.

Fixes #2505

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• [x] Unit test.

Does This PR Require a Core Repo Change?

• [x] No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• [ ] Followed the style guidelines of this project
• [ ] Changelogs have been updated
• [ ] Unit tests have been added
• [ ] Documentation has been updated

[linux-foundation-easycla[bot]]

The committers listed above are authorized under a signed CLA.

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[a-cid]

@xrmx

I've added the requested test

Have to admit that mocking RedisCluster was a challenge. Full disclosure, I ended up copying some code from https://github.com/redis/redis-py/blob/master/tests/test_cluster.py Hope that's not a problem.

[xrmx]

@a-cid please take a look at failing docker tests

[a-cid]

@xrmx

Fixed