systemd/system/sshkeys: Make execution more robust

The service failed when the unit to start was masked. Since it involves
networking, the service can fail and if it does we should restart. It
also seems that the service relied on
update-ssh-keys-after-ignition.service to run update-ssh-keys once to
create the subfolder and could possibly race with it.

Prevent execution when it has no chance to succeed because the unit to
start is masked but in all other cases try to restart on failure. Also
order behind update-ssh-keys-after-ignition.service.

systemd/system/sshkeys.service

@@ -1,4 +1,7 @@
 [Unit]
+# Don't race and we also want to rely on the folder to be created
+After=update-ssh-keys-after-ignition.service
+
 ConditionKernelCommandLine=|ignition.platform.id=packet
 ConditionKernelCommandLine=|flatcar.oem.id=packet
 ConditionKernelCommandLine=|coreos.oem.id=packet
@@ -22,6 +25,8 @@ ConditionKernelCommandLine=|coreos.oem.id=openstack
 [Service]
 Type=oneshot
 RemainAfterExit=yes
+Restart=on-failure
+ExecCondition=/usr/bin/bash -c 'if [ $("readlink -f /etc/systemd/system/coreos-metadata-sshkeys@core.service") = "/dev/null" ]; then exit 1; fi'
 ExecStart=/usr/bin/systemctl start coreos-metadata-sshkeys@core.service
 
 [Install]