'adds a group to inventory if not there already'

def add_group(self, group):

    if (group not in self.groups):
        g = Group(group)
        self.groups[group] = g
        self._groups_dict_cache = {}
        display.debug(('Added    group    %s    to    inventory' % group))
    else:
        display.debug(('group    %s    already    in    inventory' % group))
