check if variables are defined using proper ansible syntax

playbooks/roles/bastion/tasks/main.yml

@@ -47,7 +47,7 @@
       - db_host: "{{ ORA_MYSQL_HOST }}"
         db_name: "{{ ORA_MYSQL_DB_NAME }}"
         script_name: ora-rds.sh
-  when: COMMON_MYSQL_READ_ONLY_PASS
+  when: COMMON_MYSQL_READ_ONLY_PASS is defined
 
 # These templates rely on there being a global
 # read_only mongo user, you must override the default
@@ -67,4 +67,4 @@
         db_name: "{{ FORUM_MONGO_DATABASE }}"
         db_port: "{{ FORUM_MONGO_PORT }}"
         script_name: forum-mongo.sh
-  when: COMMON_MONGO_READ_ONLY_PASS
+  when: COMMON_MONGO_READ_ONLY_PASS is defined