Pin psutil<2 to avoid psutil dependency

See pytest-dev/pytest-xdist#585

home/jobs/OMERO-test-integration/config.xml

@@ -21,7 +21,9 @@ source $WORKSPACE/.venv3/bin/activate
 pip install https://github.com/ome/zeroc-ice-py-centos7/releases/download/0.2.1/zeroc_ice-3.6.5-cp36-cp36m-linux_x86_64.whl
 pip install -U pip future setuptools
 pip install markdown
-pip install mox3 pytest pytest-django pytest-xdist
+# Avoid installing psutil for now
+# https://github.com/pytest-dev/pytest-xdist/issues/585
+pip install mox3 pytest pytest-django 'pytest-xdist<2'
 pip install tables
 pip install jinja2
 pip install PyYAML