Temporary pin the Manila jobs nodeset to Focal

As per the community wide goal to migrate the CI/CD from
Ubuntu Focal to Ubuntu jammy, devstack change was merged, image got
migrated on Nov 18. But Manila jobs are failing on Ubuntu Jammy.

To unblock the Manila CI we need to pin the jobs to ubuntu focal,
until all the jobs are fixed.

Change-Id: Ia235cf28382947a392151f2914ce2dda964b46a6

zuul.d/manila-tempest-jobs.yaml

@@ -165,6 +165,7 @@
 
 - job:
     name: manila-tempest-plugin-lvm-base
+    nodeset: openstack-single-node-focal
     description: |
       Test LVM multibackend (DHSS=False) in a 4+6 (dual-stack) devstack
       environment with IPv6 control plane endpoints.
@@ -352,6 +353,7 @@
 
 - job:
     name: manila-tempest-plugin-cephfs-native-base
+    nodeset: openstack-single-node-focal
     abstract: true
     description: Test CephFS Native (DHSS=False)
     parent: manila-tempest-plugin-base
@@ -397,6 +399,7 @@
 
 - job:
     name: manila-tempest-plugin-cephfs-nfs-base
+    nodeset: openstack-single-node-focal
     abstract: true
     description: Test CephFS NFS (DHSS=False)
     parent: manila-tempest-plugin-base
@@ -578,6 +581,7 @@
     description: |
       Test the GlusterFS driver (DHSS=False) with the native GlusterFS protocol
     parent: manila-tempest-plugin-standalone-base
+    nodeset: openstack-single-node-focal
     required-projects:
       - x/devstack-plugin-glusterfs
     vars:
@@ -610,6 +614,7 @@
     description: |
       Test the GlusterFS driver (DHSS=False) with the native NFS protocol
     parent: manila-tempest-plugin-standalone-base
+    nodeset: openstack-single-node-focal
     required-projects:
       - x/devstack-plugin-glusterfs
     vars: