Automatic merge from submit-queue (batch tested with PRs 63859, 63979). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Remove signal handler registration from pkg/kubelet

**What this PR does / why we need it**:

The goal of this change is to remove the registration of signal
handling from pkg/kubelet (i.e., library code). 
 
If you register a signal handler in `main()` to aid in a controlled
and deliberate exit then the handler registered in `pkg/kubelet` often
wins and the process exits immediately. This means all other signal
handler registrations are currently racy if `DockerServer.Start()` is
directly or indirectly invoked.

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #

**Special notes for your reviewer**:

This change also removes another signal handler registration from
`NewAPIServerCommand()`; a stop channel is now passed to this
function.

**Release note**: