Add cyborg tempest job.

The Cyborg tempest plugin has been merged in Train [1]. The
creation and deletion of VMs with this patch series are
validated with that plugin.

The plugin is being enhanced to cover other VM operations like
reboots, pause, etc. [2]

[1] https://opendev.org/openstack/cyborg-tempest-plugin
[2] https://review.opendev.org/#/c/685183/

Change-Id: Id8762d0d95aa7c90feee64eb07a50433ca6ca3d1
Blueprint: nova-cyborg-interaction

.zuul.yaml

@@ -403,6 +403,9 @@
             irrelevant-files: *dsvm-irrelevant-files
         - openstacksdk-functional-devstack:
             irrelevant-files: *dsvm-irrelevant-files
+        - cyborg-tempest:
+            irrelevant-files: *dsvm-irrelevant-files
+            voting: false
     gate:
       jobs:
         - nova-grenade-multinode