Update check_mongodb.py
Update check_mongodb.py

- Make the script really goes out with good return code
- Remove duplicate action for page_faults
a-yiorgos/nagios-plugin-mongodb,alexp789/nagios-plugin-mongodb,adrianlzt/nagios-plugin-mongodb,warrenpnz/nagios-plugin-mongodb,mzupan/nagios-plugin-mongodb,Elbandi/nagios-plugin-mongodb,hdeheer/nagios-plugin-mongodb,MingjunZhao/Mapscape-Nagios-Mongo