CI: Switch upgrade jobs to Ubuntu focal 20.04

Since Victoria supports focal, we can switch the upgrade jobs to run on
focal.

Change-Id: I8f150b443af4fb831332836f90a9c38ff61a17cc

zuul.d/jobs.yaml

@@ -151,7 +151,7 @@
 - job:
     name: kolla-ansible-ubuntu-source-upgrade
     parent: kolla-ansible-base
-    nodeset: kolla-ansible-bionic
+    nodeset: kolla-ansible-focal
     timeout: 9000
     vars:
       base_distro: ubuntu
@@ -172,7 +172,7 @@
 - job:
     name: kolla-ansible-ubuntu-source-upgrade-ceph-ansible
     parent: kolla-ansible-ceph-ansible-base
-    nodeset: kolla-ansible-bionic-multi
+    nodeset: kolla-ansible-focal-multi
     timeout: 9000
     vars:
       base_distro: ubuntu

zuul.d/nodesets.yaml

@@ -17,12 +17,6 @@
       - name: primary
         label: debian-buster-arm64
 
-- nodeset:
-    name: kolla-ansible-bionic
-    nodes:
-      - name: primary
-        label: ubuntu-bionic
-
 - nodeset:
     name: kolla-ansible-focal
     nodes: