Add 32GB nodeset definition

This change defines the 32GB node option to be used in rare cases
when a particular check requires more resources than a normal
run can provide.

Change-Id: I9ff79f98a0f1874411c0df19cb07b5473d82992a

zuul.d/nodesets.yaml

@@ -147,3 +147,13 @@
           - node-2
           - node-3
           - node-4
+
+- nodeset:
+    name: openstack-helm-single-32GB-node
+    nodes:
+      - name: primary
+        label: ubuntu-bionic-32GB
+    groups:
+      - name: primary
+        nodes:
+          - primary