Clean up libvirt XML parsing

[cgwalters]

With a helper fn.

[gemini-code-assist]

Code Review

This pull request introduces a helpful utility function, run_virsh_xml, to centralize and simplify the process of running virsh commands and parsing their XML output. This is a good refactoring that reduces code duplication and improves maintainability across several files. However, I've found one instance where the new implementation introduces a regression in error handling by silently swallowing errors that were previously propagated. My review includes a comment with a suggested fix for this issue.