Use venv when invoking tests in the pipeline

Change-Id: Ib3f894f2b96d19d0954ba3c4ce7aff9948e9c657
diff --git a/Jenkinsfile-voltha-test b/Jenkinsfile-voltha-test
index 30a4011..3a74aac 100644
--- a/Jenkinsfile-voltha-test
+++ b/Jenkinsfile-voltha-test
@@ -38,7 +38,10 @@
                     cd $WORKSPACE
                     rm -rf *.log
                     export VOLTCONFIG=/home/cord/.volt/config ; sleep 10
-                    cd $WORKSPACE/voltha-system-tests/tests
+                    cd $WORKSPACE/voltha-system-tests
+                    make vst_venv
+                    source vst_venv/bin/activate
+                    cd tests
                     robot --removekeywords wuks -d Log -V $WORKSPACE/${configBaseDir}/${configDeploymentDir}/${configFileName}.yaml -v POD_NAME:${configFileName} -v KUBERNETES_CONFIGS_DIR:$WORKSPACE/${configBaseDir}/${configKubernetesDir} functional/Voltha_PODTests.robot || true
                     kubectl get pods --all-namespaces -o jsonpath="{range .items[*].status.containerStatuses[*]}{.image}{'\\t'}{.image}{'\\n'}" | sort | uniq
                     kubectl get pods --all-namespaces -o jsonpath="{range .items[*].status.containerStatuses[*]}{.image}{'\\t'}{.imageID}{'\\n'}" | sort | uniq