Make MySQL root username configurable

While this doesn't seem to make sense on first glance it is useful for
systems which were screwed with Parallels Plesk, which renames the MySQL
root user to "admin".

This change allowes this role to be used while the server is
transitioning from Plesk to Ansible.

defaults/main.yml

@@ -1,5 +1,6 @@
 ---
 mysql_user_home: /root
+mysql_root_username: root
 mysql_root_password: root
 
 # Pass in a comma-separated list of repos to use (e.g. "remi,epel"). Used only

templates/python-my.cnf.j2

@@ -1,3 +1,3 @@
 [client]
-user=root
-password={{ mysql_root_password }}
+user={{ mysql_root_username }}
+password={{ mysql_root_password }}