Automatic merge from submit-queue (batch tested with PRs 64399, 64324, 64404, 64406, 64396). 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>.
Should use `hostProcMountinfoPath` constant in nsenter_mount.go.
**What this PR does / why we need it**:
In nsenter mounter implementation, we should read mountinfo from `/rootfs/proc/1/mountinfo` instead of `/proc/self/mountinfo`.
**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**:
`/proc/self/mountinfo` will prefix `/rootfs` on mount point path, see
```
$ mkdir /mnt/test
$ mount -t tmpfs tmpfs /mnt/test/
$ docker run -it --volume=/:/rootfs:ro,rslave --net=host --pid=host --privileged=true busybox:latest cat /rootfs/proc/1/mountinfo | grep '\/mnt\/test'
442 25 0:80 / /mnt/test rw,relatime shared:70 - tmpfs tmpfs rw
$ docker run -it --volume=/:/rootfs:ro,rslave --net=host --pid=host --privileged=true busybox:latest cat /proc/self/mountinfo | grep '\/mnt\/test'
1075 985 0:80 / /rootfs/mnt/test rw,relatime master:70 - tmpfs tmpfs rw
```
**Release note**:
```release-note
NONE
```
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