Switch Amphora jobs to use clouds with nested-virt

Seems like it's now possible to request nodes from a cloud that supports
nested virtualization. This is super cool for jobs using Amphora and
this commit attempts to switch these jobs to use it.

Depends-On: I203773de2b8c0d1b21ef3f722df7ed7da562a892
Change-Id: I950e81d3f9f23493f26d9f824d3052ed375ae62b

.zuul.d/nodesets.yaml

@@ -21,3 +21,13 @@
       - name: tempest
         nodes:
           - controller
+
+- nodeset:
+    name: kuryr-nested-virt-ubuntu-focal
+    nodes:
+      - name: controller
+        label: nested-virt-ubuntu-focal
+    groups:
+      - name: tempest
+        nodes:
+          - controller

.zuul.d/tempest-jobs.yaml

@@ -192,6 +192,7 @@
 - job:
     name: kuryr-kubernetes-tempest-amphora
     parent: kuryr-kubernetes-base-ovn
+    nodeset: kuryr-nested-virt-ubuntu-focal
     required-projects:
       - openstack/octavia
       - openstack/python-octaviaclient
@@ -231,6 +232,7 @@
 - job:
     name: kuryr-kubernetes-tempest-amphora-ovs
     parent: kuryr-kubernetes-octavia-base-ovs
+    nodeset: kuryr-nested-virt-ubuntu-focal
     vars:
       devstack_localrc:
         KURYR_EP_DRIVER_OCTAVIA_PROVIDER: amphora