STYLE: Change CLI test launch command to "SEM_LAUNCH_COMMAND"

Since the idea is to decouple the CLI build code from Slicer related
variables so that module could easily be built outside of Slicer, let's
use "SEM_LAUNCH_COMMAND" instead of "Slicer_LAUNCH_COMMAND"

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21737 3bd1e089-480b-0410-8dfb-8563597acbee