Code review comment for lp:~sinzui/juju-release-tools/validate-streams

I have a subtle change to the script. Instead of passing the args that might be passed to assemble-streams, the script now expects the caller to clearly state the expected differences.

I changed the script command line to clearly indicate when a version is added:
   --added 1.20.9 --retracted 1.20.8

Which also renamed version => added

I have changed added to be optional so that the function does not need to guess about expected differences
    check_expected_tools(old_tools, new_tools, added=None, retracted=None)

The assemble-streams script will need intelligence to know when something is added and retracted. This might not be tricky since it is configured with the reacted version and there is a check if any new tools were created.

Note I made a change to verbose. I used this script for the 1.20.10 release, and I had to check the return code because --verbose didn't clearly tell me that everything was fine. I really wanted a clear message that the content was correct.