Shib: Do need read /root/.my.cnf when creating tables

The Ansible mysql_db module mixes information from /root/.my.cnf and
information in the task. Setting an empty config_file makes sure the
/root/.my.cnf is not read

roles/shibboleth/tasks/shibboleth_database_backend.yml

@@ -59,6 +59,7 @@
     login_host: "{{ shib.db_host }}"
     state: import
     target: /tmp/shibboleth_database.sql
+    config_file: ""
   changed_when: false
   run_once: true