ros setup files lead to confined paths

A file used to setup the environment named _setup_util.py sets up a search path in CMAKE_PREFIX_PATH using the directories from the build. Although it is not a problem on amd64, it is a problem on armhf as it leads to a denial and failure to rosrun the catkin packages.

Since either way it is wrong, the CMAKE_PREFIX_PATH just needs to be loaded with the independent location, code which exists right after the initialization of this variable.