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/init-container.md

@@ -0,0 +1,42 @@
+---
+title:  初始化容器（Init Container）
+id: init-container
+date: 2018-04-12
+full_link: 
+short_description: >
+  应用容器运行前必须先运行完成的一个或多个初始化容器。 
+
+aka: 
+tags:
+- fundamental
+---
+
+<!--
+---
+title: Init Container
+id: init-container
+date: 2018-04-12
+full_link: 
+short_description: >
+  One or more initialization containers that must run to completion before any app containers run.
+
+aka: 
+tags:
+- fundamental
+---
+-->
+
+<!--
+ One or more initialization {{< glossary_tooltip text="containers" term_id="container" >}} that must run to completion before any app containers run.
+-->
+
+ 应用{{< glossary_tooltip text="容器" term_id="container" >}}运行前必须先运行完成的一个或多个初始化容器。
+
+<!--more--> 
+
+<!--
+Initialization (init) containers are like regular app containers, with one difference: init containers must run to completion before any app containers can start. Init containers run in series: each init container must run to completion before the next init container begins.
+-->
+
+初始化（init）容器像常规应用容器一样，只有一点不同：初始化（init）容器必须在应用容器启动前运行完成。
+Init 容器的运行顺序：一个初始化（init）容器必须在下一个初始化（init）容器开始前运行完成。