Checkout the targeted branches/tags from the winrepo remotes

def checkout(self):
        '''
        Checkout the targeted branches/tags from the winrepo remotes
        '''
        self.winrepo_dirs = {}
        for repo in self.remotes:
            cachedir = self.do_checkout(repo)
            if cachedir is not None:
                self.winrepo_dirs[repo.id] = cachedir