baremetal: use ignition.config.url kernel parameter

The Ignition configuration currently gets written out only once to the
OEM partition and any updates to it in the matchbox store are not
propagated to the node's Ignition environment when Ignition is forced
to run again.

Use the Ignition kernel parameter to point the node's Ignition
environment directly to matchbox where the userdata lies.

assets/terraform-modules/matchbox-flatcar/templates/install.yaml.tmpl

@@ -49,7 +49,6 @@ storage:
             wipefs -f -a "$${disk}" || echo "error: failed to wipe $${disk}"
           done
           %{~ endif ~}
-          curl --retry 10 "${ignition_endpoint}?mac=${mac_address}&os=installed" -o ignition.json
           flatcar-install \
             %{~ if install_to_smallest_disk ~}
             -s \
@@ -59,14 +58,13 @@ storage:
             -C ${os_channel} \
             -V ${os_version} \
             -o "${container_linux_oem}" \
-            ${baseurl_flag} \
-            -i ignition.json
+            ${baseurl_flag}
           udevadm settle
           OEM_DEV="$(blkid -t "LABEL=OEM" -o device)"
           mkdir -p /tmp/oemfs
           mount "$${OEM_DEV}" /tmp/oemfs
           # append to file on newly created partition, do not remove the defaults
-          echo 'set linux_append="${kernel_args}"' >> /tmp/oemfs/grub.cfg
+          echo 'set linux_append="${kernel_args} ignition.config.url=${ignition_endpoint}?mac=${mac_address}&os=installed"' >> /tmp/oemfs/grub.cfg
           echo 'set linux_console="${kernel_console}"' >> /tmp/oemfs/grub.cfg
           umount /tmp/oemfs
           systemctl reboot