Added variable for debian version, so we support jessie and stretch hosts

mysql/tasks/main.yml

 ---
 # file: roles/mysql/tasks/main.yml
 
-- name: ensure mysql packages are installed
+- name: ensure mysql packages are installed for jessie
   apt: name={{ item }} state=latest
   with_items:
     - mysql-server
     - python-mysqldb
+  when:
+    - debian_version == "jessie"
+  tags:
+    - packages
+    - mysql
+
+- name: ensure mysql packages are installed for stretch
+  apt: name={{ item }} state=latest
+  with_items:
+    - mariadb-server
+    - python-mysqldb
+  when:
+    - debian_version == "stretch"
   tags:
     - packages
     - mysql