How do I create a Mongo config file to allow access to http on port 28017
You're on RHEL6 or a derivative from your kernel version 2.6.32-431.3.1.el6.x86_64. The default firewall only allows ssh incoming. You'll need to poke a hole in your firewall. Look here for firewall tips:

http://wiki.centos.org/HowTos/Network/IPTables