Add secure sample with JDBC and data.sql

We can't easily solve the problem by not allowing Spring Security to
eagerly instantiate everything, but we can be defensive about data.sql
and make sure it is executed even if the listener isn't yet registered.

Fixes gh-1386

spring-boot-samples/spring-boot-sample-web-secure-jdbc/src/main/resources/data.sql

@@ -0,0 +1,3 @@
+insert into users (username, password, enabled) values ('user', 'user', true);
+
+insert into authorities (username, authority) values ('user', 'ROLE_ADMIN');