r.py easyblock might manage libPaths or R_LIBS_USER explicitly

[emdrago]

For installing R or R-bundle-*, the existance of local packages in the environment of the person running EB can confound the sanity check logic.
Craig addresses this via "R_LIBS_USER=/dev/null"

Another approach is when installing, take steps to manage the environment.

Does it make sense to limit the sanity check to only checking the buildpath, and to not examine any other paths?
Unfortunately, I don't work with R, so this suggestion would likely be improved through review.

[boegel]

@lexming Can you take a look at this?