Fix Ubuntu boot process

This fixes the Ubuntu boot automation, possibly by cheating and using
EFI. The previous command didn't have the right series of keys, and just
using EFI actually makes the Ubuntu and Mint boot commands nearly
identical (it seems like the names for the `initrd` are unfortunately
still just slightly different).

VirtualBox has pretty seriously improved their EFI support recently so
this should be mostly safe.

Author: laurelmay

packer/mint-build.pkr.hcl

@@ -102,6 +102,7 @@ source "virtualbox-iso" "base-build" {
   boot_wait                = "5s"
   cpus                     = 2
   disk_size                = 20480
+  firmware                 = "efi"
   format                   = "ova"
   gfx_controller           = "vmsvga"
   gfx_vram_size            = 64
@@ -173,17 +174,13 @@ build {
     output_filename = "image-${lower(var.semester)}-ubuntu"
     output_directory = "${path.cwd}/artifacts_ubuntu"
     boot_command = [
-      "<esc><wait>",
-      "<esc><wait>",
-      "<esc><wait>",
-      "<enter><wait>",
-      "/casper/vmlinuz",
+      "<esc><wait><esc><wait><esc><wait>",
+      "c<wait>",
+      "linux /casper/vmlinuz fsck.mode=skip<wait> noprompt",
       " auto url=http://{{ .HTTPIP }}:{{ .HTTPPort }}/oem-preseed.cfg",
-      " automatic-ubiquity",
-      " debug-ubiquity",
-      " keymap=us",
-      " boot=casper initrd=/casper/initrd noprompt --",
-      "<enter>"
+      " automatic-ubiquity debug-ubiquity keymap=us<enter>",
+      "initrd /casper/initrd<enter><wait>",
+      "boot<enter>"
     ]
     export_opts = [
       "--manifest",