crtools: Make fdset be an array of file descriptors

Path is not needed there -- we can call the get_image_path() in prep_cr_fdset_
routines and in parasite-syscall.c when required.

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