Check the context for the notifier and construct it if not present

def _get_notifier(config):
    '''
    Check the context for the notifier and construct it if not present
    '''
    if 'inotify.notifier' not in __context__:
        __context__['inotify.queue'] = collections.deque()
        wm = pyinotify.WatchManager()
        __context__['inotify.notifier'] = pyinotify.Notifier(wm, _enqueue)
        if ('coalesce' in config and
                isinstance(config['coalesce'], bool) and
                config['coalesce']):
            __context__['inotify.notifier'].coalesce_events()
    return __context__['inotify.notifier']