mounts: Mount / in new mount namespace as slave
mounts: Mount / in new mount namespace as slave

The container shouldn't affect master's mount tree. This
is done by marking / as slave.

Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

cyrillos/xemul-libct,LK4D4/libct,LK4D4/libct,hallyn/libct,cyrillos/xemul-libct,avagin/libct,cyrillos/xemul-libct,LK4D4/libct,hallyn/libct,xemul/libct,xemul/libct,xemul/libct,avagin/libct,cyrillos/xemul-libct,hallyn/libct,xemul/libct,avagin/libct