Make COMPILE_DEFINITIONS property target scoped

vtk_module_test(...) was setting COMPILE_DEFINITIONS
as a directory property, this scope is too broad.
Changed to property of target.

Change-Id: I778ba899198d9e239ed2b12eafc6af81b07f16f0
Merge topic 'test-module-comp-def' into master

f7bd4f4e Make COMPILE_DEFINITIONS property target scoped