Fix check_task_flag

os.exit raises an SystemExit exception, should not call it in a generic
try except block.

scripts/check_task_flag.py

@@ -6,15 +6,15 @@
 
 TASK_KEY = sys.argv[1]
 
+done = False
 try:
     r = redis.Redis(host=os.environ["REDIS_SERVER"], db=int(os.environ["REDIS_DB"]))
     if r.exists(TASK_KEY) and r.get(TASK_KEY).decode() == "DONE":
-        sys.exit(0)
-    else:
-        sys.exit(1)
+        done = True
 except:
     cf = CloudFiles(os.environ["SCRATCH_PATH"])
     if cf.exists(f"done/{TASK_KEY}.txt"):
-        sys.exit(0)
-    else:
-        sys.exit(1)
+        done = True
+
+if not done:
+    sys.exit(1)