add global cmdline parameter

defaults/main.yml

@@ -1,5 +1,5 @@
-grub_cmdline_linux:
-grub_cmdline_linux_default: quiet
+grub_cmdline_linux: "{{ cmdline }}"
+grub_cmdline_linux_default: quiet {{ cmdline }}
 grub_disable_recovery: false
 grub_terminal: console
 boot_devices: "{{ hard_disks | map(attribute='device') | list }}"