append rather than replace with cmake properties

When configuring TestSystemCaps changed set_source_files_properties
to set_property because we need to append rather than replace
previous values. This change lets both MPI and Python report run.

Change-Id: I178523a08780253c63b2e751189d6053a04cd839
Merge topic 'sqplugin-topo-mapper-gui' into next

5a58366 append rather than replace with cmake properties