Exposed configuration of atomic requests

Added the option of overriding atomic requests without having to override the entire database configuration structure.

playbooks/roles/edxapp/defaults/main.yml

@@ -79,6 +79,7 @@ EDXAPP_MYSQL_PASSWORD: 'password'
 EDXAPP_MYSQL_PASSWORD_READ_ONLY: 'password'
 EDXAPP_MYSQL_PASSWORD_ADMIN: 'password'
 EDXAPP_MYSQL_OPTIONS: {}
+EDXAPP_MYSQL_ATOMIC_REQUESTS: True
 EDXAPP_MYSQL_REPLICA_DB_NAME: "{{ EDXAPP_MYSQL_DB_NAME }}"
 EDXAPP_MYSQL_REPLICA_USER: "{{ EDXAPP_MYSQL_USER }}"
 EDXAPP_MYSQL_REPLICA_PASSWORD: "{{ EDXAPP_MYSQL_PASSWORD }}"
@@ -825,7 +826,7 @@ edxapp_databases:
     PASSWORD: "{{ EDXAPP_MYSQL_PASSWORD }}"
     HOST: "{{ EDXAPP_MYSQL_HOST }}"
     PORT: "{{ EDXAPP_MYSQL_PORT }}"
-    ATOMIC_REQUESTS: True
+    ATOMIC_REQUESTS: "{{ EDXAPP_MYSQL_ATOMIC_REQUESTS }}"
     CONN_MAX_AGE: "{{ EDXAPP_MYSQL_CONN_MAX_AGE }}"
     OPTIONS: "{{ EDXAPP_MYSQL_OPTIONS }}"
   student_module_history: