Build openSUSE 42.3 nodepool images

openSUSE 42.3 is currently in feature freeze so it will become
the default stable release. Prepare infrastructure to handle
42.3 nodepool image builds. With this patch we can eventually
phase out 42.2 once jobs have been converged to 42.3

Change-Id: I44b1d25168c3e7f3680b486e7a3234bea53fd2bb

nodepool/nodepool.yaml

@@ -1293,3 +1293,20 @@ diskimages:
       DIB_IMAGE_CACHE: /opt/dib_cache
       QEMU_IMG_OPTIONS: compat=0.10
       DIB_GRUB_TIMEOUT: '0'
+  - name: opensuse-423
+    elements:
+      - opensuse-minimal
+      - vm
+      - simple-init
+      - openstack-repos
+      - nodepool-base
+      - cache-devstack
+      - growroot
+      - infra-package-needs
+    release: '42.3'
+    env-vars:
+      TMPDIR: /opt/dib_tmp
+      DIB_CHECKSUM: '1'
+      DIB_IMAGE_CACHE: /opt/dib_cache
+      QEMU_IMG_OPTIONS: compat=0.10
+      DIB_GRUB_TIMEOUT: '0'