Eng 6880 concurrent access

For these new tests, testing all of these extra columns in the tuple is mostly just distracting to the main point of the test. 
Reduce the column validation to just enough (like one column?) to ensure that the index cursors are not interfering with each other to cause wrong tuples to be produced or tuples to be skipped in an iteration.

A realistic edge case would be to iterate to the last expected tuple (not yet returning the null tuple) with the first cursor,
then iterating part way with the second cursor, then coming back to find that the next tuple on the first cursor is the null tuple.

It's difficult to relate the search key values with the expected result. Maybe some comments would help like "given search key X, Y expect to find rows with values A through B for column 0". If you are reusing searches from previous tests, refer back to those tests with comments like "Validate that the exact same scan tested in (the middle of) test XYZ still operates when there is a simultaneous scan like the one in (the end part of) test ABC."