Examples should run against a secure cluster

I think this repo is awesome for providing code samples! However I think it should also aspire to show how to do things The Right Way (tm). Especially given that we print out a huge warning that says to users: "eat your vegetables".

My experience working on [docs#631](https://github.com/cockroachdb/docs/issues/631) so far is teaching me that (at least for Java) doing it the "right way" is quite complex! (But in the bad, uninteresting, fiddly and hard-to-get-right way, not in any of the good ways.)

I might be able to help with some PRs once I get through the docs issue and understand this a little better, but filing this to capture.

从相关的 docs#631 issue 开始，检查 Java 示例当前如何连接到集群；此 issue 未指定任何文件、测试或入口点。明确哪些示例和安全集群设置属于范围，然后验证所选示例能否针对安全集群成功运行。

由索引模型根据 Issue 内容生成。