Automatic merge from submit-queue
Make /var/lib/kubelet as shared during startup
This is part of ~~https://github.com/kubernetes/community/pull/589~~https://github.com/kubernetes/community/pull/659
We'd like kubelet to be able to consume mounts from containers in the future, therefore kubelet should make sure that `/var/lib/kubelet` has shared mount propagation to be able to see these mounts.
On most distros, root directory is already mounted with shared mount propagation and this code will not do anything. On older distros such as Debian Wheezy, this code detects that `/var/lib/kubelet` is a directory on `/` which has private mount propagation and kubelet bind-mounts `/var/lib/kubelet` as rshared.
Both "regular" linux mounter and `NsenterMounter` are updated here.
@kubernetes/sig-storage-pr-reviews @kubernetes/sig-node-pr-reviews
@vishh
Release note:
```release-note
Kubelet re-binds /var/lib/kubelet directory with rshared mount propagation during startup if it is not shared yet.
```
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