Check if PID is still alive.

def is_alive(pidfile):
    '''
    Check if PID is still alive.
    '''
    try:
        with salt.utils.files.fopen(pidfile) as fp_:
            os.kill(int(fp_.read().strip()), 0)
        return True
    except Exception as ex:
        if os.access(pidfile, os.W_OK) and os.path.isfile(pidfile):
            os.unlink(pidfile)
        return False