Call os.kill for each child instead of the process group
    
    The patch sets the process group id to its process id. Note that this
    change raises an OSError in Glance's tests because they are run under
    Popen and using glance-control, which changes children's session ids and
    other parameters. That for, setpgid is inside a try / except and falls
    back to 0.
    
    Fixes bug 1068051
    
    Change-Id: Ie9ed044e08053d0067396138de0bd124326aa1a5