Fix bug 1168503 - Have the null constraint check correctly check identity columns on update.
Add YAML test
merge tjoneslo: Fix bug 1168503 - The code that tests the NULL constraint (UserTableRowChecker) was excluding the identity columns from the null check.

https://code.launchpad.net/~tjoneslo/akiban-server/fix-bug-1168503/+merge/159272