Fix pytest module detection for run.sh

Fix pytest module detection for run.sh

To allow concurrent invocations of pytest, it is necessary to assign
ports properly to avoid conflicts. In order to do that, pytest needs to
know a complete list of all test modules.

When pytest is invoked from run.sh, the current working directory is the
system test directory. To properly detect other tests, the conftest.py
has to look in the bin/tests/system directory, rather than the current
working directory.

(cherry picked from commit d4502206a146b00ce1f8c1fad50a024d654b25f5)