When seizeing task we need to parse /proc/pid/status for its
state, parent, signals and seccomp status.

In criu case we also parse other stuff in one go, so make
this parsing be a callback which criu will provide.
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>