rTEL does not support relative input paths

After some more testing yesterday, I figured out that rTEL does not support relative input paths (even though we state that in the README), because we do change the working directory as part of the workflow to cater the needs of Philosopher. This PR hopefully solves the problem. FYI, I have tested eTEL and mTEL modules and they both accept absolute and relative input paths. cc: @landerer @tothpet @moon