Increase cinder volume quota for cbak job

With new tests such as I281f881 being added,
cinder-tempest-plugin-cbak-ceph is failing due to
the quota limit of 10 volumes.

Increase this to 25.

Change-Id: I5c7818da89323c9de4381326882707828a7a1db2
diff --git a/.zuul.yaml b/.zuul.yaml
index 85e15bc..a9c7d7e 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -217,6 +217,8 @@
               volume_revert: True
       devstack_services:
         c-bak: true
+      devstack_localrc:
+        CINDER_QUOTA_VOLUMES: 25
 
 - job:
     name: cinder-tempest-plugin-cbak-ceph-zed