ensure the pid is an integer
ensure the pid is an integer

This avoids an attacker from overwriting any file on the host machine
ending with ".bson". I.e., by specifying a string process identifier
rather than an integer a similar bug would be hit as we had in Cuckoo
1.1 [1]. In this case the ".bson" extension is forced such that the
application of this arbitrary file overwrite is limited in scope.

[1]: https://cuckoosandbox.org/2014-10-07-cuckoo-sandbox-111.html

cuckoobox/cuckoo,cuckoobox/cuckoo,cuckoobox/cuckoo,cuckoobox/cuckoo,cuckoobox/cuckoo