Do not discard PID if sending a signal fails

Discarding the PID makes troubleshooting more difficult
for the user.  There is no reason to think the process
has exited unless we receive SIGCHLD.

Author: mnaberez

supervisor/process.py

@@ -470,7 +470,6 @@ def kill(self, sig):
                                                           self.pid, tb)
             options.logger.critical(msg)
             self.change_state(ProcessStates.UNKNOWN)
-            self.pid = 0
             self.killing = False
             self.delay = 0
             return msg
@@ -509,7 +508,6 @@ def signal(self, sig):
                                 processname, self.pid, tb)
             options.logger.critical(msg)
             self.change_state(ProcessStates.UNKNOWN)
-            self.pid = 0
             return msg
 
         return None

supervisor/tests/test_process.py

@@ -876,7 +876,7 @@ def test_kill_from_running_error(self):
             'unknown problem killing test'))
         self.assertTrue('Traceback' in options.logger.data[1])
         self.assertFalse(instance.killing)
-        self.assertEqual(instance.pid, 0)
+        self.assertEqual(instance.pid, 11) # unchanged
         self.assertEqual(instance.state, ProcessStates.UNKNOWN)
         self.assertEqual(len(L), 2)
         event1 = L[0]
@@ -1027,7 +1027,7 @@ def test_signal_from_running_error(self):
         self.assertTrue('Traceback' in options.logger.data[1])
         self.assertFalse(instance.killing)
         self.assertEqual(instance.state, ProcessStates.UNKNOWN)
-        self.assertEqual(instance.pid, 0)
+        self.assertEqual(instance.pid, 11) # unchanged
         self.assertEqual(len(L), 1)
         event = L[0]
         self.assertEqual(event.__class__, events.ProcessStateUnknownEvent)