Use Ignition to create core user

overlay/usr/lib/dracut/modules.d/40ignition-conf/base.ign

@@ -0,0 +1,19 @@
+{
+  "ignition": {
+    "version": "3.0.0"
+  },
+  "passwd": {
+    "users": [
+      {
+        "name": "core",
+        "gecos": "CoreOS Admin",
+        "groups": [
+          "adm",
+          "sudo",
+          "systemd-journal",
+          "wheel"
+        ]
+      }
+    ]
+  }
+}

overlay/usr/lib/dracut/modules.d/40ignition-conf/module-setup.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+# -*- mode: shell-script; indent-tabs-mode: nil; sh-basic-offset: 4; -*-
+# ex: ts=8 sw=4 sts=4 et filetype=sh
+
+depends() {
+    echo ignition
+}
+
+install() {
+    inst "$moddir/base.ign" \
+        "/usr/lib/ignition/base.ign"
+}

overlay/usr/lib/systemd/system-preset/42-coreos.preset

@@ -1,6 +1,5 @@
 # Presets here that eventually should live in the generic fedora presets
 enable coreos-growpart.service
-enable coreos-useradd-core.service
 enable console-login-helper-messages-*.service
 enable console-login-helper-messages-*.path
 # This one is from https://github.com/coreos/ignition-dracut