tty: add vt support, v2

/dev/ttyN are the virtual terminals which are provided
by the system with major 4 and minor 1..63.
You can run some program on ttyN by pressing alt+ctrl+FN
and running it manualy or by using open(openvt nowadays).

This patch also allows us to run all our tests from a vt.

v2, style fix + using linux/vt.h for constants

Signed-off-by: Ruslan Kuprieiev <kupruser@gmail.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>