Disable dstat service temporary in ovn scenario jobs

Multinode OVN jobs are failing very often due to bug [1] so
lets disable dstat service in those jobs for now as workaround
of the problem.

[1] https://bugs.launchpad.net/ubuntu/+source/dstat/+bug/1866619

Change-Id: Id9bb16d9e3e649e1538bc33bd1b7e8eab7e74048
Closes-Bug: #1898863

zuul.d/tempest-multinode.yaml

@@ -177,6 +177,10 @@
         q-qos: true
         neutron-segments: True
         q-port-forwarding: true
+        # NOTE(slaweq): disable dstat until bug
+        # https://bugs.launchpad.net/ubuntu/+source/dstat/+bug/1866619 will be
+        # fixed
+        dstat: false
     group-vars:
       subnode:
         devstack_services:
@@ -197,6 +201,10 @@
           q-metering: false
           q-ovn-metadata-agent: true
           tls-proxy: true
+          # NOTE(slaweq): disable dstat until bug
+          # https://bugs.launchpad.net/ubuntu/+source/dstat/+bug/1866619 will be
+          # fixed
+          dstat: false
         devstack_localrc:
           Q_AGENT: ovn
           Q_ML2_PLUGIN_MECHANISM_DRIVERS: ovn,logger