TLS support wanted

[firebat]

Is your feature request related to a problem? Please describe.
我们的系统跨机房部署，初步方案为 nginx / https 走rest接口，这就需要开发人员做许多额外的工作（协议转换，HA 等），而Router、负载均衡、这些策略在现有众多的rpc框架中已经做的很好了，只需添加TLS支持即可，再外部无法提供更多安全支持或更复杂的情况下，以最小代价达到安全通信。

Describe the solution you'd like
Bolt基于Netty实现，增加SSL支持代价较小。RpcServer 添加

bolt.ssl.switch=false|true
bolt.ssl.keystore=<keystore-file>
bolt.ssl.keystore.password=<keystore-file-password>
bolt.ssl.keystore.type=pcks12

RpcClient使用的Url增加useSSL=true，开启Netty的SslHandler。

Describe alternatives you've considered

Additional context
RpcServer容易修改，改动量比较小。

ChannelPipeline pipeline = channel.pipeline();
if (sslSwitch) {
    pipeline.addLast("sslHandler", new SslHandler(createSslContext().newEngine(channel.alloc())));
}
pipeline.addLast("decoder", codec.newDecoder());
pipeline.addLast("encoder", codec.newEncoder());

客户端需要调整的略多，AbstractConnectionFactory的ChannelInitializer需要调整，在createConnection的时候根据Url的配置去构造Handler列表。

protected Channel doCreateConnection(String targetIP, int targetPort, int connectTimeout)
                                                                                         throws Exception {
    //
    ......
    bootstrap.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, connectTimeout)
                     .handler(new ChannelInitializer<SocketChannel>() {

        @Override
        protected void initChannel(SocketChannel channel) {
            ChannelPipeline pipeline = channel.pipeline();
            if (url.useSSL()) {
                pipeline.addLast("sslHandler", new SslHandler(createSslContext().newEngine(channel.alloc())));
            }

[dbl-x]

@firebat 可以提PR来解决这个问题；目前规划版本暂无此功能。

[zongtanghu]

This feature request is much more import!We need it! @dbl-x

[killme2008]

I am working on this feature, and the PR will be created today.

[cytnju]

fixed #197