[Re]define REPO as http package repository.

        http_repo REPO

def do_http_repo(self, repo):
        '''
        [Re]define REPO as http package repository.

        http_repo REPO
        '''
        self.abort_on_missing_effective_repo_name(repo, 'http_repo')
        repo_name = self.get_effective_repo_name(repo)
        try:
            self.network.set(repo_name, REPO.TYPE, REPOTYPE.HTTP)
        except UnknownRepoError:
            self.network.define_http_repo(repo_name)
        self.network.active_repo = repo_name