It will be used for executed parasite as a daemon.
What we have previously -- the stack has been preallocated in parasite
blob itself and bootstrap procedure calculated the value needed for %rsp.

With this patch applied we provide every thread own stack as:

- find out how many threads are present
- calculate the summary size of all stacks
- when we ask dumpee to provide us memory area needed to run
  parasite code, we pass summary size needed for everything
- when parasite code is asked to run we calculate %rsp needed
  taking into account the thread number (ie offsets) and then
  setup proper %rsp via ptrace call, instead of calculating it
  in bootstrap parasite code
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>