Only setup backup when rsnapshot is configured, don't use password for root auth

Mysql doesn't need a root password to authenticate root locally. And without rsnapshot installed, configuring rsnapshot config doesn't work.

mysql/defaults/main.yml

@@ -6,3 +6,5 @@ mysql_root_password: "{{ lookup('passwordstore', 'db/{{ ansible_hostname }}-mysq
 mysql_backup_user: "backup"
 # yamllint disable-line rule:line-length
 mysql_backup_password: "{{ lookup('passwordstore', 'db/{{ ansible_hostname }}-mysql-backup create=true length=20') }}"
+
+mysql_rsnapshot: false