[datafeed] also catch EnvironmentError when trying to load the cwclientlib config file
means the config file has not been found, so fall back to the old implementation
instead of crashing.
usr/lib/PY_VERSION/*-packages/cubicweb/entities/
usr/lib/PY_VERSION/*-packages/cubicweb/ext/
usr/share/cubicweb/cubes/
usr/lib/PY_VERSION/*-packages/cubicweb/*.py