[CMake] spoof "Not Run" dashboard status

[burlen]

Can a test return a value to indicate that it could not be run?

The use case I'm thinking of is for VTK's rendering tests. When a test 
is run on a driver with known bugs, the test is skipped internally, and 
shows up as passed in the dashboard. I suspect that it's done this way 
to avoid polluting the dashboard, and it's probably a good idea to keep 
it like this. However, I think it's an issue that it's difficult to tell 
which tests are being skipped on which systems and it would be very 
useful if these tests showed up in the dashboard as not run rather than 
passed.

Burlen