zulip-puppet-apply: Exit status code 2 on puppet failure.

This allows us, when run with `--noop -f`, to differentiate between
"there are unapplied changes" and "there were puppet errors."

scripts/zulip-puppet-apply

@@ -83,6 +83,8 @@ def noop_would_change(puppet_cmd: List[str]) -> bool:
         with open(lastrun_file.name) as lastrun:
             lastrun_data = yaml.safe_load(lastrun)
             return lastrun_data.get("resources", {}).get("out_of_sync", 0) != 0
+    except subprocess.CalledProcessError:
+        sys.exit(2)
     finally:
         lastrun_file.close()
 
@@ -111,4 +113,4 @@ ret = subprocess.call([*puppet_cmd, "--detailed-exitcodes"], env=puppet_env)
 # ret = 4 => no changes, yes errors
 # ret = 6 => changes, yes errors
 if ret != 0 and ret != 2:
-    sys.exit(1)
+    sys.exit(2)