Fix undefined ceph variable in library litmus job

... and define the variable in a more common place to avoid
distributing the same definition.

Change-Id: I5fb20ffcaa36dbb13f0e73cf5f9fef705a40173b

zuul.d/litmus.yaml

@@ -25,6 +25,8 @@
       - ^setup.cfg$
       - ^setup.py$
       - ^tox.ini$
+    vars:
+      ceph: quincy
 
 - job:
     name: puppet-openstack-litmus-module-base
@@ -44,7 +46,6 @@
     nodeset: centos-9-stream
     vars:
       puppet_gem_version: 7.16.0
-      ceph: quincy
 
 - job:
     name: puppet-openstack-litmus-7.16-ubuntu-jammy
@@ -53,7 +54,6 @@
     voting: false
     vars:
       puppet_gem_version: 7.16.0
-      ceph: quincy
 
 - job:
     name: puppet-openstack-litmus-latest-ubuntu-jammy
@@ -62,7 +62,6 @@
     voting: false
     vars:
       puppet_gem_version: latest
-      ceph: quincy
 
 - job:
     name: puppet-openstack-libraries-litmus-7.16-centos-9-stream