Run os.kill for all child pids even after some of them are down

Right now, we come out of the iteration in case of failure
while trying to kill a child pid. This may result in some of
the child pids staying alive.

Change-Id: I18d58fcefec2bbdae4ae9bf73594939ade241b52

Author: OswinNathanial

git/cmd.py

@@ -618,7 +618,10 @@ def _kill_process(pid):
             try:
                 os.kill(pid, SIGKILL)
                 for child_pid in child_pids:
-                    os.kill(child_pid, SIGKILL)
+                    try:
+                        os.kill(child_pid, SIGKILL)
+                    except OSError:
+                        pass
                 kill_check.set()    # tell the main routine that the process was killed
             except OSError:
                 # It is possible that the process gets completed in the duration after timeout