dracut/30ignition: Reboot the system after ignition if kargs.d exists

As mentioned in https://github.com/coreos/ignition-dracut/issues/81#issuecomment-494888494,
this change adds a service that checks for the presence of `/etc/ostree/kargs.d` and redeploys
then reboots the system if it exists.

Closes: #81

dracut/30ignition/ignition-apply-kargs.service

@@ -0,0 +1,13 @@
+[Unit]
+Description=Reboot after Ignition to apply kargs
+Documentation=https://github.com/coreos/ignition-dracut
+DefaultDependencies=false
+Before=ignition-complete.target
+
+# Make sure user configs have kargs files
+After=ignition-files.service
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/usr/sbin/ignition-apply-kargs

dracut/30ignition/ignition-apply-kargs.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+set -euo pipefail
+
+# Checks if kernel argument directory exists,
+# then redeploy and reboot the system if it exists
+reboot_if_kargs_dir_exists() {
+    local REFSPEC=( $(ostree refs --repo /sysroot/ostree/repo) )
+    if [ -d /sysroot/etc/ostree/kargs.d ]
+    then
+        ostree admin deploy REFSPEC
+        exec systemctl reboot
+    fi
+}
+
+reboot_if_kargs_dir_exists

dracut/30ignition/module-setup.sh

@@ -35,6 +35,9 @@ install() {
     inst_script "$moddir/ignition-setup.sh" \
         "/usr/sbin/ignition-setup"
 
+    inst_script "$moddir/ignition-apply-kargs.sh" \
+        "/usr/sbin/ignition-apply-kargs"
+
     # Distro packaging is expected to install the ignition binary into the
     # module directory.
     inst_simple "$moddir/ignition" \
@@ -53,6 +56,7 @@ install() {
     install_ignition_unit ignition-mount.service
     install_ignition_unit ignition-files.service
     install_ignition_unit ignition-remount-sysroot.service
+    install_ignition_unit ignition-apply-kargs.service
 
     # needed for openstack config drive support
     inst_rules 60-cdrom_id.rules