ENH: Tcl tests should not fail if VTK_DATA_ROOT is missing.

A test should run without VTK_DATA_ROOT unless it needs input data
from VTK_DATA_ROOT. Tests that have image baselines should still run
unless they need input data.

rtImage.tcl is modified to skip baseline comparisons if VTK_DATA_ROOT
is not defined.

CMakeLists.txt files are converted to use add_test_tcl macro for
consistency.

CMakeLists.txt files are changed to isolate tests that need input
data.

This was tested as follows:
1) configured a build with VTK_DATA_ROOT undefine
   ctest -R Tcl-
   154 tests passed
2) configured a build with VTK_DATA_ROOT defined
   ctest -R Tcl-
   390 tests passed

This means that 390-154 = 236 tcl tests require input data

Change-Id: I9067a3e3e2a710ddf353f0181cc7b22a85b5ef10
Merge topic 'TestingWithoutData_Tcl' into master

c5ab6fda ENH: Tcl tests should not fail if VTK_DATA_ROOT is missing.