Update federation jobs to use ubuntu focal

This change is consistent with updates we landed in keystone:

  fb86048d0a83cc6f2b5dcf78124ed12202902092

Change-Id: Ibd1d6624fc3addbe60c7218766d80cb43ad732bc
diff --git a/.zuul.yaml b/.zuul.yaml
index 87f496f..11a43a8 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -5,16 +5,16 @@
     check:
       jobs:
         - keystone-dsvm-py3-functional
-        - keystone-dsvm-py3-functional-federation-opensuse15:
+        - keystone-dsvm-py3-functional-federation-ubuntu-focal:
             voting: false
-        - keystone-dsvm-py3-functional-federation-opensuse15-k2k
+        - keystone-dsvm-py3-functional-federation-ubuntu-focal-k2k
         - keystone-dsvm-py3-functional-ussuri
         - keystone-dsvm-py3-functional-train
         - keystone-dsvm-py3-functional-stein
     gate:
       jobs:
         - keystone-dsvm-py3-functional
-        - keystone-dsvm-py3-functional-federation-opensuse15-k2k
+        - keystone-dsvm-py3-functional-federation-ubuntu-focal-k2k
 
 - job:
     name: keystone-dsvm-py3-functional-ussuri