tmt: Add du cmd to check disk usage

Signed-off-by: Pragyan Poudyal <pragyanpoudyal41999@gmail.com>

Author: Johan-Liebert1

crates/xtask/src/tmt.rs

@@ -564,6 +564,8 @@ fn run_plan(
     // Log disk usage after each test run to help diagnose "no space left on device" failures
     println!("Disk usage after plan {}:", plan);
     let _ = cmd!(sh, "df -h").run();
+    let _ = cmd!(sh, "du -h /var/* -d 1").run();
+    println!("==========================================");
 
     // Clean up VM regardless of test result (unless --preserve-vm is set)
     cleanup_vm();