Apply contraints to tempest plugins

This commit applies the constraints for the tempest plugin installation
so they won't go over the upper reqs.

Closes-Bug: 1763436
Change-Id: I5cf91157bbdae79dec01d5b3db32efea21f1b2b7

Author: danielmellado

lib/tempest

@@ -646,7 +646,7 @@ function install_tempest {
 function install_tempest_plugins {
     pushd $TEMPEST_DIR
     if [[ $TEMPEST_PLUGINS != 0 ]] ; then
-        tox -evenv-tempest -- pip install $TEMPEST_PLUGINS
+        tox -evenv-tempest -- pip install -c $REQUIREMENTS_DIR/upper-constraints.txt $TEMPEST_PLUGINS
         echo "Checking installed Tempest plugins:"
         tox -evenv-tempest -- tempest list-plugins
     fi