cloudccl: allow external connection tests to be run in parallel

[rhu713]

Currently external connection tests read and write to the same path in cloud storage. Add a random uint64 as part of the path so that test runs have unique paths and can be run in parallel.

Fixes: #107407

Release note: None

[cockroach-teamcity]

This change is 

[msbutler]

looks good! Could you do one test run via TC to confirm everything passes?

[msbutler]

LGTM. Could you trigger one run the nightlies just to make sure everything passes?

[rhu713]

Done! Manually triggered cloud unit test run here: https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Nightlies_CloudUnitTests/11255551?hideProblemsFromDependencies=false&hideTestsFromDependencies=false&expandBuildChangesSection=true

[rhu713]

bors r+

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

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error creating merge commit from 38f086c to blathers/backport-release-22.2-108465: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 22.2.x failed. See errors above.

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