There is a lot of command-line-task documentation in here and I think some of it can be moved to ctrl_mpexec where the command line options for pipetask match (such as long-log and show config).

Whilst looking at the show options as part of the documentation, I have realized that we should not be continuing on to run pipelines if a show option is used. Previous implementations always stop processing (although cmdLineTask had an option to override that). Andy Salnikov thinks that it did stop correctly before we moved to click and so I should add that back.

Andy Salnikov can you please take a look at this? In pipe_base it's mostly deletions but I moved some configuration docs over to ctrl_mpexec and that resulted in me completely changing how "--show" worked and so there are patches in ctrl_mpexec and daf_butler to fix those.

Trivial changes in pipe_tasks and ctrl_pool (disabling flake8 testing to prevent code loading) and also pipe_drivers now can import the deprecated gen3 Task even if gen2 classes don't exist.

pipe_base PR is not showing up on Jira: https://github.com/lsst/pipe_base/pull/274

Looks great, thanks for restoring --show behavior!