Increase swap size to 4GB

The ceph jobs are failing apparently due to mysqld being reaped by
the oom reaper, which of course cascades into service failures due
to db errors.  Increasing the swap size allows the jobs to run to
completion.

Default is 1G.  See other patches on topic: increase-swap to see
how 4G was determined.

Change-Id: Ibf2a7fd2a305d04303b1288a6f1faebfc9ffd6de
diff --git a/.zuul.yaml b/.zuul.yaml
index 251e92c..96e7d75 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -150,6 +150,7 @@
       Integration tests that runs with the ceph devstack plugin, py3
       and enable the backup service.
     vars:
+      configure_swap_size: 4096
       devstack_local_conf:
         test-config:
           $TEMPEST_CONFIG: