Bug 17654: Add tests to enforce swagger definition files integrity

Bug 17654: Add tests to enforce swagger definition files integrity

The swagger definition error we found on bug 17651 should have been
caught earlier with tests.

Now we are testing for nullable columns.

QA: Have a look at the FIXME

Test plan:
Apply without 17651 (revert if already pushed)
The tests won't pass
On top of 17651 the tests will pass

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Katrin Fischer  <katrin.fischer@bsz-bw.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>