Update the I_S tables IT tests to be a little broader to cover more
cases. This is instead of the YamlIT approach to testing the ITs.
Add more tests, as `LIMIT 0` does all the processing without returning
any rows (which can be too variable to check).
Check table with null values rather than real values to verify row
count.
merge tjoneslo: Update the I_S tables IT tests to be a little broader to cover more.

Merge pull request #1469 from tjoneslo/sql-layer/test-is-tables-in-yamlit
https://github.com/FoundationDB/sql-layer/pull/1469