improve diagnostics from bazel_linter.py (#101445)
improve diagnostics from bazel_linter.py
Summary:
This was swallowing stderr on errors and trying to just parse an empty
string from stdout.
Test Plan: Verify with subsequent broken diff.
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Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/pytorch/pytorch/pull/101445).
* #101406
* #101405
* #101928
* __->__ #101445
* #101744
Pull Request resolved: https://github.com/pytorch/pytorch/pull/101445
Approved by: https://github.com/huydhn
