BUG: Fix subject hierarchy node creation bug and automatic tests

Bug reported in this thread
http://slicer-users.65878.n3.nabble.com/DICOM-RT-Export-td4028406.html
fixed, now subject hierarchy nodes are also created before the user visits the SH module (only if auto-generate is turned on, or if loaded from DICOM).

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23824 3bd1e089-480b-0410-8dfb-8563597acbee