Replace the timeout process kill with a terminate.

The kill operation is never a good choice for stopping a subprocess - it
does not give the subprocess any chance to clean up. It's more usual to
try a terminate and later kill if the process did not stop. More
importantly to me, the kill method isn't present in the python 2
multiprocessing module.

pythonfuzz/fuzzer.py

@@ -158,7 +158,7 @@ def start(self):
             buf = self._corpus.generate_input()
             parent_conn.send_bytes(bytes(buf))
             if not parent_conn.poll(self._timeout):
-                self._p.kill()
+                self._p.terminate()
                 logging.info("=================================================================")
                 logging.info("timeout reached. testcase took: {}".format(self._timeout))
                 self.write_sample(buf, prefix='timeout-')