COMP: Add execption for vtkJSONWriter

The TestSetGet.tcl scrip is failing on platforms that have
Module_vtkIOGeoJSON:BOOL=ON
The method GetOutputStdString is only valid when WriteToOutputString
is on. This patch adds GetOutputStdString to the exceptions.

Change-Id: I149f34c0a9d769ad963db99c80dce3469b6a93e3
Merge topic 'TestSetGetException' into master

0bee648b COMP: Add execption for vtkJSONWriter