Close #12114: fix a potential deadlock in packaging.util._find_exe_version()

Avoid also zombi processes: Popen.communicate() calls its wait() method.
diff --git a/Lib/packaging/util.py b/Lib/packaging/util.py
index 71ce819..bf31c31 100644
--- a/Lib/packaging/util.py
+++ b/Lib/packaging/util.py
@@ -464,7 +464,7 @@
         return None
     pipe = Popen(cmd, shell=True, stdout=PIPE, stderr=PIPE)
     try:
-        stdout, stderr = pipe.stdout.read(), pipe.stderr.read()
+        stdout, stderr = pipe.communicate()
     finally:
         pipe.stdout.close()
         pipe.stderr.close()