kvm: adhere to Debian's grub layout

This adopts our anti-CPU-mitigation configuration to use Debian's
expected grub paths and programs.

roles/kvm/files/cpu-mitigations.cfg

@@ -0,0 +1 @@
+GRUB_CMDLINE_LINUX="noibrs noibpb nopti nospectre_v2 nospectre_v1 l1tf=off nospec_store_bypass_disable no_stf_barrier mds=off tsx=on tsx_async_abort=off mitigations=off"

roles/kvm/files/grub-mitigations.conf

@@ -1 +0,0 @@
-noibrs noibpb nopti nospectre_v2 nospectre_v1 l1tf=off nospec_store_bypass_disable no_stf_barrier mds=off mitigations=off

roles/kvm/tasks/main.yml

@@ -76,22 +76,16 @@
   shell: grep -c Intel /proc/cpuinfo
   register: intel_check
 
-- name: Create sysconfig directory
-  file:
-    path: /etc/sysconfig
-    state: directory
-  when: intel_check.stdout != "0"
-
 - name: Install grub config to disable CPU mitigations
   copy:
-    src: grub-mitigations.conf
-    dest: /etc/sysconfig/grub
+    src: cpu-mitigations.cfg
+    dest: /etc/default/grub.d/cpu-mitigations.cfg
     mode: 0644
   register: grub-mitigations
   when: intel_check.stdout != "0"
 
 - name: Regenerate grub's config file
-  shell: grub-mkconfig
+  shell: update-grub
   notify:
     - reboot
   when: grub-mitigations.changed