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ARROW-16417: [C++][Python] Segfault in test_exec_plan.py / test_joins

This builds on top of #13035 which is also important for avoiding segmentation faults.  On top of that there were a few more problems:

 * The python was using `SourceNodeOptions::FromTable` which is a rather dangerous method (mainly useful for unit testing) as it doesn't share ownership of the input table (even worse, it takes a const ref).  Python was not keeping the table alive and it was maybe possible for the table to deleted out from under the plan (I'm not entirely sure this was causing issues but it seemed risky).  I switched to TableSourceNode which shares ownership of the table (and is a bit more efficient).
 * Setting use_threads to False did nothing because `_perform_join` was not passing the arg on to `execplan`.
 * When fixing the above and running with `use_threads=False` it was creating a single thread executor but the current best practice is to pass in nullptr.
 * Finally, the actual bug was my improper fix in #12894 .  I had still left a small window open for `End` to be called between `Submit` and `AddTask` which would allow the task to be submitted but not participate in setting `finished` on the node.

Closes #13036 from westonpace/bugfix/ARROW-16417--segfault-in-python-join

Lead-authored-by: Weston Pace <weston.pace@gmail.com>
Co-authored-by: David Li <li.davidm96@gmail.com>
Signed-off-by: David Li <li.davidm96@gmail.com>