Output build log on testing related integration test failures

In service of tracking down flaky test failures like #1334, dump the
build/test run log when a testing related integration test fails.

Author: plemarquand

test/integration-tests/testexplorer/utilities.ts

@@ -160,7 +160,9 @@ export function assertTestResults(
             skipped: (state.skipped ?? []).sort(),
             errored: (state.errored ?? []).sort(),
             unknown: 0,
-        }
+        },
+        "Test run results do not match expected results, test run output:\n" +
+            testRun.runState.output.join("\n")
     );
 }