Silence output to console during boot

Eliminating the output to the serial console, boot time[1] of 2 levels
nested kubevirt vm is 1.8 times faster.

   bare metal -> drenv vm -> minikube vm -> kubevirt vm

system    nested    before    after
-----------------------------------
libvirt1       0        4s       4s
libvirt1       1       10s      10s
libvirt2       2       45s      25s
vmware         2       80s      55s
kubevirt       2     >150s      85s

This probably means there is something wrong in the way serial console
is handled in kubevirt. Until this is improved we can use this change
to speed up testing DR with kubvirt.

[1] time since vm is reported ready until `virtctl ssh` succeeds,
    measured using `test/addons/kubevirt/test`

Thanks: Peter Lauterbach <pelauter@redhat.com>
Signed-off-by: Nir Soffer <nsoffer@redhat.com>

test/vms/cirros/Makefile

@@ -21,6 +21,8 @@ $(disk):
 	virt-customize --add $(work) \
 		--copy-in ../ramen:/tmp \
 		--run-command "/tmp/ramen/install" \
+		--run-command "sed -i 's/console=tty1/quiet/' /boot/grub/menu.lst" \
+		--run-command "sed -i 's/console=ttyS0//' /boot/grub/menu.lst" \
 		--delete "/tmp/ramen"
 	qemu-img convert -f qcow2 -O qcow2 -c $(work) $@