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/cluster-architect.md

@@ -0,0 +1,37 @@
+---
+title: 集群架构师（Cluster Architect）
+id: cluster-architect
+date: 2018-04-12
+full_link: 
+short_description: >
+  集群架构师负责设计集群的基础设施，可能包含一个或多个 Kubernetes 集群。
+
+aka: 
+tags:
+- user-type
+---
+
+<!--
+---
+title: Cluster Architect
+id: cluster-architect
+date: 2018-04-12
+full_link: 
+short_description: >
+  A person who designs infrastructure that involves one or more Kubernetes clusters.
+
+aka: 
+tags:
+- user-type
+---
+-->
+
+ 集群架构师负责设计集群的基础设施，可能包含一个或多个 Kubernetes 集群。
+
+<!--more--> 
+
+<!--
+Cluster architects are concerned with best practices for distributed systems, for example&#58; high availability and security.
+-->
+
+集群架构师要具备分布式系统的最佳实践经验，例如：高可用性和安全性。