The exit status of a killed process should be None

[raczben]

Describe the bug
The exit status of a killed process should be None

To Reproduce

import wexpect
import time

def test_expect_wait_after_termination():
    """Ensure wait on a process terminated by kill -9.
    based on IsAliveTestCase::test_expect_wait_after_termination()"""
    
    p = wexpect.spawn('sleep 3')
    assert p.isalive()
    p.kill(9)
    time.sleep(1)

    # when terminated, the exitstatus is None, but p.signalstatus
    # and p.terminated reflects that the kill -9 nature.
    exitstat = p.wait()
    print('exitstat: {}'.format(exitstat))
    assert exitstat is None
        
test_expect_wait_after_termination()

Expected behavior
The exit status of a killed process should be None

Environment:

• OS Name Microsoft Windows 10 Home
• Version 10.0.18362 Build 18362
• Python 3.7.5
• wexpect v2.3.9