Fix use of `run_ctest_` variables

[RafaelPalomar]

This commit includes a new check based on the run_ctest_submit variable when submitting PARTS build. Without this fix, you could try to disable submission to dashboard but the build information will still appear submitted.

This commit modifies the logic of the script to decouple the building of the Slicer package and its upload. This is to support cases where the Slicer package needs to be built, but won't be uploaded. Not having this in place forces the generated package to be uploaded.