Made MongodbHandlerPool a singleton again

cdplib/db_handlers/MongodbHandler.py

@@ -22,7 +22,7 @@ import numpy as np
 sys.path.append(os.getcwd())
 from cdplib.log import Log
 from cdplib.db_migration.ParseJsonSchema import ParseJsonSchema
-
+from cdplib.Singleton_Threadsafe import SingletonThreadsafe
 
 class MongodbHandlerPool(metaclass=SingletonThreadsafe):
 #class MongodbHandlerPool():