[COMMANDS] Add vcpu monitor command

This patch adds monitor sub-command to vcpu command. The new
command periodically prints CPU, RAM, VAPOOL, and VCPU status
just like linux top command. It uses VT100 console commands
to refresh screen and reset cursor position periodically. The
commands works fine with serial port, telnet connection, and
framebuffer character device.

This patch is inspired from patch "[DAEMONS] Add a monitor
daemon, with compatibility with framebuffers." submitted
by Jimmy.

Signed-off-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Jimmy Durand Wesolowski <jimmy.durand-wesolowski@openwide.fr>