[CI/Build] For ppc64le, disabled tests for now and addressed space issues

[npanpaliya]

For ppc64le, vllm tests have been failing due to which the build and test job is failing. For now, we have disabled the tests so that atleast build can be enabled for ppc64le, while we work on the tests failure. This PR also addresses the CI agent disk space issues.

[github-actions]

👋 Hi! Thank you for contributing to the vLLM project.
Just a reminder: PRs would not trigger full CI run by default. Instead, it would only run fastcheck CI which starts running only a small and essential subset of CI tests to quickly catch errors. You can run other CI tests on top of those by going to your fastcheck build on Buildkite UI (linked in the PR checks section) and unblock them. If you do not have permission to unblock, ping simon-mo or khluu to add you in our Buildkite org.

Once the PR is approved and ready to go, your PR reviewer(s) can run CI to test the changes comprehensively before merging.

To run CI, PR reviewers can do one of these:

• Add ready label to the PR
• Enable auto-merge.

🚀

[sumitd2]

@khluu
@npanpaliya is from my team and she will take care of the Power build and test issues from now on. So please tag her in future when you need to delegate the task to us. I have tested the CI job locally and its passing.

Please also enable the Power CI after you merge this.

[DarkLight1337]

Sorry for the delay.

Ping: @khluu in case you missed it.

[npanpaliya]

Thank you @DarkLight1337 for merging this PR.

[sumitd2]

@DarkLight1337 Is the PR check for ppc64le now enabled?

[DarkLight1337]

@simon-mo can you enable it?

[sumitd2]

@simon-mo can you enable it?

@simon-mo Have we enabled it?