bundlespec: fix the "streamv2" and "streamv3-exp" variant
In c4aab3661f25, we broken this feature by adding unicode instead of bytes to
the dictionary.
On the other hand, this feature was never tested, so augment the tests to tests
this.
# name space package to host third party extensions
import pkgutil
__path__ = pkgutil.extend_path(__path__, __name__)