Prevent .hypothesis artifacts in system test directories

Prevent .hypothesis artifacts in system test directories

The "run.sh" script, used by "make test", changes the working
directory to the system test directory before executing pytest.
If the test drops hypothesis artifacts while running, this
can cause spurious test failures due to an apparent mismatch
between the contents of the system test directory and the
temporary pytest directory. This has been addressed by having
"run.sh" call pytest from the parent directory instead.