Fix unbound local when an error occurs before pool is initialized (#156750)

Pull Request resolved: https://github.com/pytorch/pytorch/pull/156750
Approved by: https://github.com/jamesjwu

test/run_test.py

@@ -1859,6 +1859,7 @@ def run_tests(
         "If running on CI, add the 'keep-going' label to your PR and rerun your jobs."
     )
 
+    pool = None
     try:
         for test in selected_tests_serial:
             options_clone = copy.deepcopy(options)
@@ -1921,8 +1922,9 @@ def run_tests(
         del os.environ["NUM_PARALLEL_PROCS"]
 
     finally:
-        pool.terminate()
-        pool.join()
+        if pool:
+            pool.terminate()
+            pool.join()
 
     return