Reload systemd config files before starting kubelet.

In some environments, the os image comes with preloaded kubelet.service,
so we need to reload systemctl configs to make changes effective.

cluster/gce/gci/configure-helper.sh

@@ -1170,6 +1170,7 @@ ExecStart=${kubelet_bin} \$KUBELET_OPTS
 WantedBy=multi-user.target
 EOF
 
+  systemctl daemon-reload
   systemctl start kubelet.service
 }