'Determines whether the given filesystem path contains a hookable plugin.
All sub-directories that contain ``loading_point_filename`` are considered
plugins.
:type   plugin_path:    string
:param  plugin_path:    relative or absolute filesystem path to the
potential plugin
:rtype:                 bool
:returns:               True if the path contains a plugin'

def is_plugin(self, plugin_path):

    if (not super(HookPluginManager, self).is_plugin(plugin_path)):
        return False
    if (self.loading_point_filename not in os.listdir(plugin_path)):
        return False
    return True
