Add and switch to the newly created opensuse-15 nodeset

opensuse-150 nodeset is referring to openSUSE 15.0, which is still in
maintenance but openSUSE 15.1 has been released already. "opensuse-15"
is going to refer to the "latest openSUSE 15.x" build released and
working for OpenStack going forward, so add this nodeset and use
it by default going forward.

Change-Id: I427e1d56384841770deb9c56cd56cbffb2df456b

zuul.d/jobs.yaml

@@ -58,7 +58,7 @@
 - job:
     name: openstack-infra-base-integration-opensuse15
     parent: openstack-infra-base-integration
-    nodeset: opensuse-150
+    nodeset: opensuse-15
 
 - job:
     name: openstack-infra-base-integration-opensuse-tumbleweed
@@ -211,9 +211,9 @@
     nodeset:
       nodes:
         - name: primary
-          label: opensuse-150
+          label: opensuse-15
         - name: secondary
-          label: opensuse-150
+          label: opensuse-15
       groups:
         - name: switch
           nodes:

zuul.d/nodesets.yaml

@@ -23,18 +23,26 @@
       - name: gentoo-17-0-systemd
         label: gentoo-17-0-systemd
 
+# Deprecated, please use opensuse-15 going forward
 - nodeset:
     name: opensuse-423
     nodes:
       - name: opensuse-423
         label: opensuse-423
 
+# Deprecated, please use opensuse-15 going forward
 - nodeset:
     name: opensuse-150
     nodes:
       - name: opensuse-150
         label: opensuse-150
 
+- nodeset:
+    name: opensuse-15
+    nodes:
+      - name: opensuse-15
+        label: opensuse-15
+
 - nodeset:
     name: opensuse-tumbleweed
     nodes: