restore: support SYSV IPC vma

This patch introduces the following changes:
1) writing of shmid value into vma_area->fd instead of
   waiting for shared memory region is open by parent,
   reopen it and dump fd.
2) new syscall support: sys_shmat
3) use sys_shmat() to map memory region in restorer's
   mapping function if vma flag VMA_AREA_SYSVIPC is set.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@openvz.org>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>