Changes to nvidia.service to allow ordering on the subsequent services

When changed to oneshot, the subsequent services wiill actually wait for the nvidia.service to finish, i.e. wait for drivers to be installed. The subsequent services can be configured to wait for nvidia.service. This needs to be coupled with
RemainAfterExit=yes to ensure it doesn't get kicked-off automatically again.
Solves : flatcar/Flatcar#1136

sdk_container/src/third_party/coreos-overlay/x11-drivers/nvidia-drivers/files/units/nvidia.service

@@ -2,9 +2,11 @@
 Description=NVIDIA Configure Service
 Wants=network-online.target
 After=network-online.target
+Before=containerd.target
 
 [Service]
-Type=simple
+Type=oneshot
+RemainsAfterExit=true
 Restart=no
 Environment=PATH=/opt/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin
 ExecStart=/usr/lib/nvidia/bin/setup-nvidia