upgrade k8s code to 1.16

[cofyc]

Feature Request

Is your feature request related to a problem? Please describe:

Keep up to date with the latest k8s code.

• compatibility is guaranteed by CI and stability tests (tested in k8s 1.12.x), in the future, we can add more test jobs for other Kubernetes versions (e2e: test against multiple Kubernetes versions #1008)
• latest k8s e2e framework (k8s.io/kubernetes/test/e2e/framework) is well designed and can be reused in projects outside of core Kubernetes, we can leverage this framework to write our e2e tests
• easier to adopt libraries which depends on newer k8s code

Describe the feature you'd like:

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy:

[cofyc]

• rename pingcap.com to pingcap (rename pingcap.com directory to pingcap #1061)
  • the higher version of code-generator will use the name of this directory as the package name, so the domain cannot be used

[yylt]

the pingcap/pd not use go mod manage module at v2.1.0-beta+incompatible
pd use etcd@v0.0.0-20180530235116-2b3aa7e1d49d， but k8s@1.16 use etcd@v3.3.15 , it will conflict

[cofyc]

yes, it's a problem, we need to upgrade PD

[gregwebs]

PD should not be required to align dependencies with k8s, particularly one like etcd. We just need to reference some API code that should be abstracted over PD dependencies.
I think the problem is that we are referencing a PD package that imports many things. Instead the PD API definitions should be moved to a package with minimal dependencies.

[cofyc]

I think the problem is that we are referencing a PD package that imports many things. Instead the PD API definitions should be moved to a package with minimal dependencies.

yes, that will be better

[aylei]

I think the problem is that we are referencing a PD package that imports many things. Instead the PD API definitions should be moved to a package with minimal dependencies.

@gregwebs I'm working on proposing this to PD and TiDB.

@cofyc Because it takes time for PD to merge the change and release a new version, I've copied the config type definition and get rid of the pd/server dependency for now in #1048