Automatic merge from submit-queue (batch tested with PRs 65899, 65900). 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>.
fix CRI socket validatioin
**What this PR does / why we need it**:
CRI socket doesn't have to be an absolute path, it should be an url.
However, attempt to use it as an url in 'kubeadm init' command line
causes this validation error:
$ sudo ./kubeadm init --cri-socket unix:///var/run/crio/crio.sock
nodeRegistration.criSocket: Invalid value:
"unix:///var/run/crio/crio.sock": path is not absolute
Fixed by adding ValidateSocket function and using it in the
ValidateNodeRegistrationOptions check instead of ValidateAbsolutePath.
**Which issue(s) this PR fixes** :
[#928](https://github.com/kubernetes/kubeadm/issues/928)
**Release note**:
```release-note
NONE
```
c174e4121f