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/pod-lifecycle.md

@@ -0,0 +1,42 @@
+---
+title: Pod 生命周期
+id: pod-lifecycle
+date: 2019-02-17
+full-link: /zh/docs/concepts/workloads/pods/pod-lifecycle/
+related:
+ - pod
+ - container
+tags:
+ - fundamental
+short_description: >
+  关于 Pod 在其生命周期中处于哪个阶段的更高层次概述。
+---
+
+<!--
+title: Pod Lifecycle
+id: pod-lifecycle
+date: 2019-02-17
+full-link: /docs/concepts/workloads/pods/pod-lifecycle/
+related:
+ - pod
+ - container
+tags:
+ - fundamental
+short_description: >
+  A high-level summary of what phase the Pod is in within its lifecyle.
+-->
+
+<!--
+A high-level summary of what phase the Pod is in within its lifecyle.
+-->
+关于 Pod 在其生命周期中处于哪个阶段的更高层次概述。
+
+<!--more-->
+
+<!--
+The [Pod Lifecycle](/docs/concepts/workloads/pods/pod-lifecycle/) is defined by the states or phases of a Pod. There are five possible Pod phases: Pending, Running, Succeeded, Failed, and Unknown. A high-level description of the Pod state is summarized in the [PodStatus](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#podstatus-v1-core) `phase` field.
+-->
+[Pod 生命周期](/zh/docs/concepts/workloads/pods/pod-lifecycle/) 是关于 Pod
+处于哪个阶段的概述。包含了下面5种可能的的阶段: Running、Pending、Succeeded、
+Failed、Unknown。关于 Pod 的阶段的更高级描述请查阅
+[PodStatus](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#podstatus-v1-core) `phase` 字段。