kubeadm: Detect CRIs automatically

In order to allow for a smoother UX with CRIs different than Docker, we have to
make the --cri-socket command line flag optional when just one CRI is
installed.

This change does that by doing the following:

- Introduce a new runtime function (DetectCRISocket) that will attempt to
  detect a CRI socket, or return an appropriate error.
- Default to using the above function if --cri-socket is not specified and
  CRISocket in NodeRegistrationOptions is empty.
- Stop static defaulting to DefaultCRISocket. And rename it to
  DefaultDockerCRISocket. Its use is now narrowed to "Docker or not"
  distinguishment and tests.
- Introduce AddCRISocketFlag function that adds --cri-socket flag to a flagSet.
  Use that in all commands, that support --cri-socket.
- Remove the deprecated --cri-socket-path flag from kubeadm config images pull
  and deprecate --cri-socket in kubeadm upgrade apply.

Signed-off-by: Rostislav M. Georgiev <rostislavg@vmware.com>

cmd/kubeadm/app/phases/kubelet/BUILD

@@ -12,7 +12,6 @@ go_library(
     visibility = ["//visibility:public"],
     deps = [
         "//cmd/kubeadm/app/apis/kubeadm:go_default_library",
-        "//cmd/kubeadm/app/apis/kubeadm/v1beta1:go_default_library",
         "//cmd/kubeadm/app/componentconfigs:go_default_library",
         "//cmd/kubeadm/app/constants:go_default_library",
         "//cmd/kubeadm/app/images:go_default_library",

cmd/kubeadm/app/phases/kubelet/flags.go

@@ -26,7 +26,6 @@ import (
 	"github.com/pkg/errors"
 	"k8s.io/klog"
 	kubeadmapi "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm"
-	kubeadmapiv1beta1 "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/v1beta1"
 	"k8s.io/kubernetes/cmd/kubeadm/app/constants"
 	"k8s.io/kubernetes/cmd/kubeadm/app/images"
 	kubeadmutil "k8s.io/kubernetes/cmd/kubeadm/app/util"
@@ -74,7 +73,7 @@ func WriteKubeletDynamicEnvFile(cfg *kubeadmapi.InitConfiguration, registerTaint
 func buildKubeletArgMap(opts kubeletFlagsOpts) map[string]string {
 	kubeletFlags := map[string]string{}
 
-	if opts.nodeRegOpts.CRISocket == kubeadmapiv1beta1.DefaultCRISocket {
+	if opts.nodeRegOpts.CRISocket == constants.DefaultDockerCRISocket {
 		// These flags should only be set when running docker
 		kubeletFlags["network-plugin"] = "cni"
 		driver, err := kubeadmutil.GetCgroupDriverDocker(opts.execer)