Allow all interfaces to listen for MongoDB in CentOS 6.6

To allow all interfaces to listen for MongoDB in CentOS 6.6,

comment out the `bind_ip` as follows:

sudo vi /etc/mongod.conf

# Listen to local interface only. Comment out to listen on all interfaces.
#bind_ip=127.0.0.1

Restart the MongoDB server (mongod) as follows:

sudo /sbin/service mongod start