Add failing tests showing problem with <fullTestName>_DISABLE then fix (TriBITS #47)

There was a defect where <fullTestName>_DISABLE=ON would only disable a test
if test tracing was enabled.  These new tests show the problem.

I then fixed the behavior in the same commit.  To see the defect, just revert
the change to the file TribitsAddTestHelpers.cmake.