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/container-lifecycle-hooks.md

@@ -0,0 +1,38 @@
+---
+title: 容器生命周期钩子（Container Lifecycle Hooks）
+id: container-lifecycle-hooks
+date: 2018-10-08
+full_link: /zh/docs/concepts/containers/container-lifecycle-hooks/
+short_description: >
+  生命周期钩子暴露容器管理生命周期中的事件，允许用户在事件发生时运行代码。
+
+aka: 
+tags:
+- extension
+---
+<!--
+---
+title: Container Lifecycle Hooks
+id: container-lifecycle-hooks
+date: 2018-10-08
+full_link: /docs/concepts/containers/container-lifecycle-hooks/
+short_description: >
+  The lifecycle hooks expose events in the container management lifecycle and let the user run code when the events occur.
+
+aka:
+tags:
+- extension
+---
+-->
+
+  生命周期钩子暴露{{< glossary_tooltip text="容器" term_id="container" >}}管理生命周期中的事件，允许用户在事件发生时运行代码。
+  <!--
+  The lifecycle hooks expose events in the {{< glossary_tooltip text="Container" term_id="container" >}}container management lifecycle and let the user run code when the events occur.
+  -->
+
+<!--more--> 
+
+针对容器暴露了两个钩子：PostStart 在容器创建之后立即执行，PreStop 在容器停止之前立即阻塞并被调用。
+<!--
+Two hooks are exposed to Containers: PostStart which executes immediately after a container is created and PreStop which is blocking and is called immediately before a container is terminated.
+-->