Be able to override the mongo bind ip.

playbooks/roles/mongo/defaults/main.yml

 mongo_logappend: true
 mongo_version: 2.4.7
-mongo_bind_ip: 127.0.0.1
 mongo_port: "27017"
 mongo_extra_conf: ''
 mongo_key_file: '/etc/mongodb_key'
@@ -21,6 +20,7 @@ MONGO_USERS:
     database: edxapp
 
 MONGO_CLUSTERED: !!null
+MONGO_BIND_IP: 127.0.0.1
 
 ##
 

playbooks/roles/mongo/templates/mongodb.conf.j2

@@ -13,7 +13,7 @@ logappend={{ mongo_logappend }}
    otherwise only to the specified local ip.
 #}
 {% if mongo_clustered is not defined %}
-bind_ip = {{ mongo_bind_ip }}
+bind_ip = {{ MONGO_BIND_IP }}
 {% endif %}
 
 port = {{ mongo_port }}