Right now memzone (stack and sigframe) sit on thread args, which
are allocated independently from rst-mem.

In the next patches task and thread args will be moved on rst-mem
and will get unmapped by restorer at the end. Since both stack and
sigframe are required even after rst-mem unmap, memzon should live
independelntly.

The new restorer blob layout will be described in the next patch.
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>