Avoid a race condition in test_rebind.py

If tor terminates due to SIGNAL HALT before test_rebind.py calls
tor_process.terminate(), an OSError 3 (no such process) is thrown.

Fixes part of bug 27968 on 0.3.5.1-alpha.

changes/bug27968

@@ -0,0 +1,3 @@
+  o Minor bugfixes (testing):
+    - Avoid hangs and race conditions in test_rebind.py.
+      Fixes bug 27968; bugfix on 0.3.5.1-alpha.

src/test/test_rebind.py

@@ -6,6 +6,7 @@ import socket
 import os
 import time
 import random
+import errno
 
 def try_connecting_to_socksport():
     socks_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
@@ -88,6 +89,14 @@ try_connecting_to_socksport()
 
 control_socket.sendall('SIGNAL HALT\r\n'.encode('utf8'))
 
-time.sleep(0.1)
+wait_for_log('exiting cleanly')
 print('OK')
-tor_process.terminate()
+
+try:
+    tor_process.terminate()
+except OSError as e:
+    if e.errno == errno.ESRCH: # errno 3: No such process
+        # assume tor has already exited due to SIGNAL HALT
+        print("Tor has already exited")
+    else:
+        raise