Adds a kubeadm config images pull command

This command will use crictl or docker to pull images locally.

The dockerfall back is needed because in some cases the kubelet is not
yet running so there is no CRI dockershim socket available.

Fixes kubernetes/kubeadm#812

Signed-off-by: Chuck Ha <ha.chuck@gmail.com>

docs/.generated_docs

@@ -60,6 +60,7 @@ docs/admin/kubeadm_completion.md
 docs/admin/kubeadm_config.md
 docs/admin/kubeadm_config_images.md
 docs/admin/kubeadm_config_images_list.md
+docs/admin/kubeadm_config_images_pull.md
 docs/admin/kubeadm_config_upload.md
 docs/admin/kubeadm_config_upload_from-file.md
 docs/admin/kubeadm_config_upload_from-flags.md
@@ -135,6 +136,7 @@ docs/man/man1/kubeadm-alpha-phase.1
 docs/man/man1/kubeadm-alpha.1
 docs/man/man1/kubeadm-completion.1
 docs/man/man1/kubeadm-config-images-list.1
+docs/man/man1/kubeadm-config-images-pull.1
 docs/man/man1/kubeadm-config-images.1
 docs/man/man1/kubeadm-config-upload-from-file.1
 docs/man/man1/kubeadm-config-upload-from-flags.1

docs/admin/kubeadm_config_images_pull.md

@@ -0,0 +1,3 @@
+This file is autogenerated, but we've stopped checking such files into the
+repository to reduce the need for rebases. Please run hack/generate-docs.sh to
+populate this file.

docs/man/man1/kubeadm-config-images-list-images.1

@@ -0,0 +1,3 @@
+This file is autogenerated, but we've stopped checking such files into the
+repository to reduce the need for rebases. Please run hack/generate-docs.sh to
+populate this file.

docs/man/man1/kubeadm-config-images-pull.1

@@ -0,0 +1,3 @@
+This file is autogenerated, but we've stopped checking such files into the
+repository to reduce the need for rebases. Please run hack/generate-docs.sh to
+populate this file.