Fix warning on MySQL >=5.5

I always got this warning:

```Warning: Using unique option prefix pass instead of password is deprecated and will be removed in a future release. Please use the full name instead.```

(http://www.serveridol.com/2013/11/19/mysql-dump-warning-using-unique-option-prefix-pass-instead-of-password-is-deprecated/)
for every mysql command I do.
I don't know, when this password option was introduced, so it might break on earlier versions of MySQL.

templates/root_dot_my.cnf.j2

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