Disable most kernel log messages during boot

Adding the quiet[1] option disables most kernel log messages during boot
These message are not needed normally and available in dmesg if needed
later.

With this change the ramen service boot time is up to 1.47 times faster.

machine    nested     before    after
-------------------------------------
laptop          0     1.55s     1.39s
laptop          1     4.73s     3.28s
server          2    32.79s    22.33s

[1] https://www.kernel.org/doc/html/v4.14/admin-guide/kernel-parameters.html

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

test/vms/cirros/Makefile

@@ -22,6 +22,7 @@ $(disk):
 	virt-customize --add $(work) \
 		--copy-in ../ramen:/tmp \
 		--run-command "/tmp/ramen/install" \
+		--run-command "sed -i 's/^\(kernel .*\)$$/\1 quiet/' /boot/grub/menu.lst" \
 		--delete "/tmp/ramen"
 	qemu-img convert -f qcow2 -O qcow2 -c $(work) $@