bump nova-lvm to use 8G of swap from 4G

nova-lvm ocationally has OOM events causing
g-api to get killed. This can result in test failures
with a 502 form glance so we bump the swap to 8G
like the ceph jobs to avoid that.

Change-Id: Ib88f9feb692ee440b8f73e9b3dca56c08dadb665

.zuul.yaml

@@ -311,6 +311,8 @@
       - ^tools/.*$
       - ^tox.ini$
     vars:
+      # Increase the swap size to avoid OOM errors when running the tests.
+      configure_swap_size: 8192
       # We use the "all" environment for tempest_test_regex and
       # tempest_exclude_regex.
       tox_envlist: all