Fixed grub2 config to work without a vga card

- Try to set up both gfxterm and serial term, but if either fails,
   continue with the other.

installer/resources/grub/grub.cfg

@@ -23,8 +23,15 @@ insmod part_msdos
 
 # Set up display
 set gfxmode=auto
-terminal_output gfxterm serial_com0
-terminal_input console serial_com0
+terminal_output gfxterm
+terminal_input console
+
+# Try to set up serial
+serial --unit=0 --speed=9600
+terminal_output --append serial
+terminal_input --append serial
+
+# Set up appearance
 background_image /boot/grub/splash.png
 loadfont /boot/grub/unicode.pf2