Automatic merge from submit-queue (batch tested with PRs 40392, 39242, 40579, 40628, 40713)
fixed bug #36988 -- kubeadm join crashes when using multiple API endpoints
**What this PR does / why we need it**:
Simple bug fix for #36988 (kubeadm crashes when trying to join nodes to a master with multiple API endpoints) -- stopChan was getting closed multiple times, once per endpoint. Moved the close into the once.Do(...)
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*:
fixes#36988
**Special notes for your reviewer**:
this is my first kubernetes commit, just getting familiar with the process, so any/all feedback is appreciated
**Release note**:
updated pkg "k8s.io/kubernetes/pkg/client/clientset_generated/internalclientset" to "k8s.io/kubernetes/pkg/client/clientset_generated/release_1_5" because the type that bootstrap.go:126 checkAPIEndpoint requires changed as well as *internalversion.CertificatesClient in csr_test.go:69
