fixing bad merge for mongo defaults

playbooks/roles/mongo/defaults/main.yml

-mongo_dbpath: /var/lib/mongodb
-mongo_logpath: /var/log/mongodb/mongodb.log
 mongo_logappend: true
 mongo_version: 2.4.7
 mongo_bind_ip: 127.0.0.1
 mongo_extra_conf: ''
 mongo_key_file: '/etc/mongodb_key'
 mongo_repl_set: rs0
-mongo_cluster_members: 
+mongo_cluster_members:
 
 mongo_data_dir: "{{ data_dir }}/mongo"
+mongo_log_dir: "{{ log_dir }}/mongo"
 mongo_app_dir: "{{ app_dir }}/mongo"
-mongo_dbpath: "{{ mongo_data_dir }}/mongodb"
 mongo_user: mongodb
 MONGO_USERS:
   - user: cs_comments_service
@@ -19,3 +17,6 @@ MONGO_USERS:
   - user: exdapp
     password: password
     database: edxapp
+
+mongo_logpath: "{{ mongo_log_dir }}/mongodb.log"
+mongo_dbpath: "{{ mongo_data_dir }}/mongodb"