TDMLRunner not detecting expected errors

While working on enabling defineVariables to have non-constant expressions, I ran into a few cases where expected errors were occurring, but were not being detected by TDMLRunner. Instead, the error occurred and the stacktrace from the exception is simply printed out, causing the test to fail even though the TDML test case was expecting that error.

See tests test_circular_defineVariable_err and test_defineVariable_ref_noDefault_err in daffodil-test/src/test/scala/org/apache/daffodil/section07/variables/TestVariables.scala which are currently commented out.