Use constraints when creating venv for grenade

As a followup for change I6a8cffdc86c895eebe4269c5cd37841325566c54
let's use branch specific upper constraints when running tests in
grenade.

Change-Id: I71f8398b6aa57b7c1910750b8e048825383e3d9a
(cherry picked from commit 39d653fa57)

.zuul.yaml

@@ -150,7 +150,7 @@
         h-eng: true
         heat: true
       # We do run a list of tests after upgrade. This is just to bypass the req from parent.
-      tempest_test_regex: ^heat_tempest_plugin\.tests\.functional\.test_nova_server_networks
+      tempest_test_regex: ^tempest\.api\.identity\.v3\.test_tokens
       tox_envlist: all
       devstack_plugins:
         heat: https://opendev.org/openstack/heat

devstack/upgrade/resources.sh

@@ -64,7 +64,11 @@ function _run_heat_integrationtests {
     # Run set of specified functional tests
     UPGRADE_TESTS=upgrade_tests.list
     _write_heat_integrationtests $UPGRADE_TESTS
-
+    export UPPER_CONSTRAINTS_FILE=$DEST/requirements/upper-constraints.txt
+    export TOX_CONSTRAINTS_FILE=$UPPER_CONSTRAINTS_FILE
+    export HEAT_TEMPEST_PLUGIN=$DEST/heat-tempest-plugin
+    sudo git config --system --add safe.directory $HEAT_TEMPEST_PLUGIN
+    tox -evenv-tempest -- pip install -c$UPPER_CONSTRAINTS_FILE $HEAT_TEMPEST_PLUGIN
     tox -evenv-tempest -- stestr --test-path=$DEST/heat/heat_integrationtests --top-dir=$DEST/heat \
         --group_regex='heat_tempest_plugin\.tests\.api\.test_heat_api[._]([^_]+)' \
         run --whitelist-file $UPGRADE_TESTS