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

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

defaults/main.yml

@@ -6,6 +6,7 @@ mariadb:
 #    mysql:
 #      host: localhost
 #      password: foobar
+#      plugin: unix_socket # instead of password for password-less authentication
 #      priv: *.*:USAGE
   dbs: {}
 #    database:

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 }}"