code: def fetch_assets(self):
          
          # allow overwrites from the commandline
          packages = set(
              env.instance.config.get('bootstrap-packages', '').split())
          packages.update(['python27'])
          cmd = env.instance.config.get('bootstrap-local-download-cmd', 'wget -c -O "{0.local}" "{0.url}"')
          items = sorted(self.bootstrap_files.items())
          for filename, asset in items:
              if asset.url:
                  if not exists(dirname(asset.local)):
                      os.makedirs(dirname(asset.local))
                  local(cmd.format(asset))
              if filename == 'packagesite.txz':
                  # add packages to download
                  items.extend(self._fetch_packages(asset.local, packages))
docs: download bootstrap assets to control host.
          If present on the control host they will be uploaded to the target host during bootstrapping.