try to hide a bug in tesh
It seems to lose the CWD for some reasons. Here is a log example:
[Tesh/INFO] change directory to /builds/workspace/SimGrid/build_mode/ModelChecker/node/simgrid-ubuntu-xenial-32/build/SimGrid-3.21.90/examples/python/actor-create
[...]
[actor-create.tesh:3] python3 /builds/workspace/SimGrid/build_mode/ModelChecker/node/simgrid-ubuntu-xenial-32/build/SimGrid-3.21.90/examples/python/actor-create/actor-create.py
[...]
+[...] [xbt/CRITICAL] Unable to open 'actor-create_d.xml' from '/builds/workspace/SimGrid/build_mode/ModelChecker/node/simgrid-ubuntu-xenial-32/build/SimGrid-3.21.90/examples/python'
