Switch language name 'zh' to 'zh-cn'

This is the first step to rename 'zh' to 'zh-cn'. There are several reasons why we rename the language name.

- The upstream docsy theme changed the language name, leading to many warnings during site build;
  The side-effect is that the i18n strings are no longer working.
- We believe renaming the language is the right thing to do, because this move can make room for other variants of Chinese language, such as 'zh-tw', 'zh-sg' etc.

There would be several follow-ups to this PR, such as fixing the intra-site links, adding redirects etc.

We will lock up changes to zh/zh-cn pages for the moment, until this one gets in.

This PR is based on commit cdad0a7342.

content/zh-cn/docs/reference/glossary/managed-service.md

@@ -0,0 +1,46 @@
+---
+title: 托管服务
+id: managed-service
+date: 2018-04-12
+full_link: 
+short_description: >
+  由第三方供应商负责维护的一种软件产品。
+
+aka: 
+tags:
+- extension
+---
+
+<!--
+title: Managed Service
+id: managed-service
+date: 2018-04-12
+full_link: 
+short_description: >
+  A software offering maintained by a third-party provider.
+
+aka: 
+tags:
+- extension
+-->
+
+<!--
+ A software offering maintained by a third-party provider.
+-->
+由第三方供应商负责维护的一种软件产品。
+
+<!--more--> 
+
+<!--
+Some examples of Managed Services are AWS EC2, Azure SQL Database, and
+GCP Pub/Sub, but they can be any software offering that can be used by an application.
+[Service Catalog](/docs/concepts/extend-kubernetes/service-catalog/) provides a way to
+list, provision, and bind with Managed Services offered by
+{{< glossary_tooltip text="Service Brokers" term_id="service-broker" >}}.
+-->
+托管服务的一些例子有 AWS EC2、Azure SQL 数据库和 GCP Pub/Sub 等，
+不过它们也可以是可以被某应用使用的任何软件交付件。
+[服务目录](/zh/docs/concepts/extend-kubernetes/service-catalog/)
+提供了一种方法用来列举、制备和绑定到
+{{< glossary_tooltip text="服务代理商（Service Brokers）" term_id="service-broker" >}}
+所提供的托管服务。