Split the CR_FD_ bits into per-task and global ones and replace
of CR_FD_DESC_NOPSTREE with CR_FD_DESC_TASK, which is explicit
set of per-task bits.

The CR_FD_DESC_NS will appear soon.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>