Add FIPS job for ubuntu

A multinode-fips job is added, which inherits from multinode.
This job provides a subscription key to enable a Ubuntu Advantage
subscription to allow us to test FIPS.

This secret is passed through to the multinode (parent job) through
the pass-to-parent boolean.

Change-Id: I470d7b7b0773d0be1e3971bc02d23ea61f80f162

zuul.d/jobs.yaml

@@ -1263,3 +1263,14 @@
 
       The testing is done for Ubuntu Xenial.
     nodeset: ubuntu-xenial
+
+- job:
+    name: openstack-multinode-fips
+    parent: multinode-fips
+    description: |
+      Multinode job with fips enabled and passing
+      the ubuntu_fips_token needed for UA subscription.
+    secrets:
+      - secret: openstack_ubuntu_fips
+        name: ubuntu_fips_token
+        pass-to-parent: true