Small fix for previous MySQL PR merge on Ansible 2.

Author: geerlingguy

tasks/main.yml

@@ -27,7 +27,7 @@
 
 - name: Check if MySQL packages were installed.
   set_fact:
-    mysql_install_packages: "{{ rh_mysql_install_packages.changed or deb_mysql_install_packages.changed }}"
+    mysql_install_packages: "{{ (rh_mysql_install_packages is defined and rh_mysql_install_packages.changed) or (deb_mysql_install_packages is defined and deb_mysql_install_packages.changed) }}"
 
 # Configure MySQL.
 - include: configure.yml