Unset attribute on the active/default repo

def do_unset(self, attribute):
        '''
        Unset attribute on the active/default repo
        '''
        self.abort_on_invalid_active_repo('unset')
        if not attribute:
            raise ShellError('command "unset" requires a non-empty attribute')
        self.network.unset(self.network.active_repo, attribute)