Automatic merge from submit-queue (batch tested with PRs 40168, 40165, 39158, 39966, 40190)
CRI: upgrade protobuf to v3
For #38854, this PR upgrades CRI protobuf version to v3, and also updated related packages for confirming to new api.
**Release note**:
```
CRI: upgrade protobuf version to v3.
```
This allows runtimes in different packages (dockertools, rkt, kuberuntime) to
share the same logic. Before this change, only dockertools support this
feature. Now all three packages support image pull throttling.
New flag --container-runtime-endpoint (overrides --container-runtime)
is introduced to kubelet which identifies the unix socket file of
the remote runtime service. And new flag --image-service-endpoint is
introduced to kubelet which identifies the unix socket file of the
image service.