Wait for containerd installation in GCE scripts

Prior to running the `kube-node-installation.service`, the containerd
installation should be complete as the k8s installation may have
dependencies on containerd and related binaries (e.g ctr). Add
wants/after systemd directives to ensure
`kube-node-installation.service` will only start after containerd
installation completes.

Signed-off-by: David Porter <porterdavid@google.com>

contrib/gce/cloud-init/master.yaml

@@ -75,7 +75,8 @@ write_files:
     content: |
       [Unit]
       Description=Download and install k8s binaries and configurations
-      After=network-online.target
+      After=network-online.target containerd.target
+      Wants=network-online.target containerd.target
 
       [Service]
       Type=oneshot

contrib/gce/cloud-init/node.yaml

@@ -69,7 +69,8 @@ write_files:
     content: |
       [Unit]
       Description=Download and install k8s binaries and configurations
-      After=network-online.target
+      After=network-online.target containerd.target
+      Wants=network-online.target containerd.target
 
       [Service]
       Type=oneshot