Add "plugin" option for users and allow to omit password

Set plugin to "unix_socket" to allow password-less socket-based authentication.

tasks/main.yml

@@ -28,7 +28,8 @@
     login_unix_socket: /var/run/mysqld/mysqld.sock
     name: "{{ item.key }}"
     host: "{{ item.value.host | default('localhost') }}"
-    password: "{{ item.value.password }}"
+    password: "{{ item.value.password | default(omit) }}"
+    plugin: "{{ item.value.plugin | default(omit) }}"
     priv: "{{ item.value.priv | default('*.*:USAGE') }}"
   with_dict: "{{ mariadb.users }}"