tests: add ignition.kargs.skipreboot test

This test verifies that if a kernel argument that is set as "should_exist"
in the Ignition config already exists on the kernel command line of the machine
then we can skip the reboot when applying kernel arguments but we must still
update the BLS configs to make it permanent.

tests/kola/ignition/kargs/skipreboot/config.bu

@@ -0,0 +1,5 @@
+variant: fcos
+version: 1.4.0
+kernel_arguments:
+  should_exist:
+    - foobar

tests/kola/ignition/kargs/skipreboot/data/commonlib.sh

@@ -0,0 +1 @@
+../../../../data/commonlib.sh

tests/kola/ignition/kargs/skipreboot/test.sh

@@ -0,0 +1,43 @@
+#!/bin/bash
+set -xeuo pipefail
+# kola: { "platforms": "qemu", "appendFirstbootKernelArgs": "foobar" }
+# This test verifies that if a kernel argument that is set as "should_exist"
+# in the Ignition config already exists on the kernel command line of the machine
+# then we can skip the reboot when applying kernel arguments but we must still
+# update the BLS configs to make it permanent. This is Scenario B from
+# the documentation in 35coreos-ignition/coreos-kargs.sh.
+#
+# - platforms: qemu
+#   - appendFirstbootKernelArgs is only supported on qemu.
+# - appendFirstbootKernelArgs: foobar
+#   - The kernel argument to apply transiently only on the first boot.
+
+. $KOLA_EXT_DATA/commonlib.sh
+
+kargchecks() {
+    if ! grep foobar /proc/cmdline; then
+        fatal "missing expected kernel arg in kernel cmdline"
+    fi
+    if ! grep foobar /boot/loader/entries/*.conf; then
+        fatal "missing expected kernel arg in BLS config"
+    fi
+}
+
+case "${AUTOPKGTEST_REBOOT_MARK:-}" in
+  "")
+      kargchecks
+      # If this file exists then reboot was skipped. See
+      # 35coreos-ignition/coreos-kargs.sh
+      if [ ! -e /run/coreos-kargs-changed ]; then
+          fatal "missing file that should exist if no reboot happened"
+      fi
+      # Now reboot the machine and verify the kernel argument persists
+      /tmp/autopkgtest-reboot nextboot
+      ;;
+  nextboot)
+      kargchecks
+      ;;
+  *) fatal "unexpected mark: ${AUTOPKGTEST_REBOOT_MARK}";;
+esac
+
+ok "Ignition kargs skip reboot"