Use .pytest rundir hook for disconnection test

By leaving the test config's rundir as default, parsl/tests/conftest.py will
reassign that attribute to a dynamically generated directory under
.pytest/parsltest-current

Author: benclifford

parsl/tests/test_htex/test_disconnected_blocks.py

@@ -26,7 +26,6 @@ def local_config():
                 ),
             )
         ],
-        run_dir="/tmp/test_htex",
         max_idletime=0.5,
         strategy='htex_auto_scale',
     )