Disable GLOBAL_VENV and disable "telemetry-dsvm-integration-train"

* Devstack recently introduced the functionality to use a single venv[1]
but some devstack plugins in telemetry project are not compatible with
this change.

This disables the option as a short term workaround.

* Tempest CI job "telemetry-dsvm-integration-train" for Train release
fails due to
```
Obtaining file:///opt/stack/nova
nova requires Python '>=3.8' but the running Python is 3.6.9
```
Train release of Nova and Heat projects have reached EOL which are
fetched while running this job. If any issues are identified in these
releases fixing them might not be possible.

[1] https://review.opendev.org/c/openstack/devstack/+/558930

Change-Id: I01ed2c96395baf294aa84e4f989ab82f9b387fc4
diff --git a/.zuul.yaml b/.zuul.yaml
index f4f7774..3b7f0de 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -94,6 +94,7 @@
         CEILOMETER_BACKEND: "gnocchi"
         CEILOMETER_PIPELINE_INTERVAL: 15
         CEILOMETER_ALARM_THRESHOLD: 6000000000
+        GLOBAL_VENV: False
       devstack_local_conf:
         test-config:
           $TEMPEST_CONFIG:
@@ -101,11 +102,11 @@
               disable_ssl_certificate_validation: True
       tempest_test_regex: telemetry_tempest_plugin
       tox_envlist: all
+      branches: ^(?!stable/(ocata|pike|queens|rocky|stein)).*$
 
 - job:
     name: telemetry-dsvm-integration
     parent: telemetry-tempest-base
-    branches: ^(?!stable/(ocata|pike|queens|rocky|stein|train)).*$
 
 - job:
     name: telemetry-dsvm-integration
@@ -135,7 +136,6 @@
 - job:
     name: telemetry-dsvm-integration-ipv6-only
     parent: devstack-tempest-ipv6
-    branches: ^(?!stable/(ocata|pike|queens|rocky|stein)).*$
     description: |
       Telemetry devstack tempest tests job for IPv6-only deployment
     required-projects: *base_required_projects
@@ -153,6 +153,7 @@
     parent: telemetry-dsvm-integration
     nodeset: openstack-single-node-bionic
     override-checkout: stable/train
+    voting: false
     vars:
       devstack_localrc:
         USE_PYTHON3: True