cypress: use DJANGO_SETTINGS_MODULE if defined when running django commands

jobs/templates/includes/stage-cypress-tests.groovy.j2

@@ -15,10 +15,10 @@ stage('Cypress tests') {
           rm -f swh-web-test*.sqlite3*
 
           # apply django migrations and create users (will produce swh-web-test.sqlite3 file)
-          python{{cypress_python_version}} swh/web/manage.py migrate --settings=swh.web.settings.tests
+          python{{cypress_python_version}} swh/web/manage.py migrate --settings=${DJANGO_SETTINGS_MODULE:-swh.web.settings.tests}
           for create_users_script in swh/web/tests/create_test_*
           do
-            cat $create_users_script | python{{cypress_python_version}} swh/web/manage.py shell --settings=swh.web.settings.tests
+            cat $create_users_script | python{{cypress_python_version}} swh/web/manage.py shell --settings=${DJANGO_SETTINGS_MODULE:-swh.web.settings.tests}
           done
 
           # build swh-web static assets in test mode (for code coverage)
@@ -56,7 +56,7 @@ stage('Cypress tests') {
                 cp swh-web-test.sqlite3 swh-web-test{{ n }}.sqlite3
 
                 # run django server on a dedicated port for that test runner and wait for it to be up
-                python{{cypress_python_version}} swh/web/manage.py runserver --nostatic --settings=swh.web.settings.tests 0.0.0.0:500{{ n }}&
+                python{{cypress_python_version}} swh/web/manage.py runserver --nostatic --settings=${DJANGO_SETTINGS_MODULE:-swh.web.settings.tests} 0.0.0.0:500{{ n }}&
                 wait-for-it -t 90 localhost:500{{ n }}
 
                 # execute cypress tests