TE-2861 Use correct version of Django in tests (openedx#20271)

scripts/xdist/prepare_xdist_nodes.sh

@@ -14,13 +14,21 @@ else
     XDIST_GIT_FETCH_STRING="$XDIST_GIT_BRANCH:$XDIST_GIT_BRANCH"
 fi
 
+# Install the correct version of Django depending on which tox environment (if any) is in use
+if [[ -z ${TOX_ENV+x} ]] || [[ ${TOX_ENV} == 'null' ]]; then
+    DJANGO_REQUIREMENT="-r requirements/edx/django.txt"
+else
+    DJANGO_REQUIREMENT=$(pip freeze | grep "^[Dd]jango==")
+fi
+
 ip_list=$(<pytest_task_ips.txt)
 for ip in $(echo $ip_list | sed "s/,/ /g")
 do
     container_reqs_cmd="ssh -o StrictHostKeyChecking=no ubuntu@$ip 'cd /edx/app/edxapp;
     git clone --branch master --depth 1 --no-tags -q https://github.com/edx/edx-platform.git; cd edx-platform;
     git fetch --depth=1 --no-tags -q origin ${XDIST_GIT_FETCH_STRING}; git checkout -q ${XDIST_GIT_BRANCH};
-    source /edx/app/edxapp/edxapp_env; pip install -qr requirements/edx/testing.txt; mkdir reports' & "
+    source /edx/app/edxapp/edxapp_env;
+    pip install -q ${DJANGO_REQUIREMENT} -r requirements/edx/testing.txt; mkdir reports' & "
 
     cmd=$cmd$container_reqs_cmd
 done

tox.ini

@@ -54,7 +54,7 @@ passenv =
     XDIST_NUM_TASKS
     XDIST_REMOTE_NUM_PROCESSES
 deps =
-    django111: Django>=1.11,<2
+    django111: -r requirements/edx/django.txt
     django20: Django>=2.0,<2.1
     django21: Django>=2.1,<2.2
     -r requirements/edx/testing.txt