Fix typo with DEVSTACK_LOCAL_CONFIG for nodepool-dsvm job
Fix typo with DEVSTACK_LOCAL_CONFIG for nodepool-dsvm job

We want to preserve the previous settings for DEVSTACK_LOCAL_CONFIG,
so append not replace.

Change-Id: I8ecfc6871aa1bae09013337a8f9d812b83c41464
Signed-off-by: Paul Belanger <e7139c8e6c4ea75cc1c287ce081b2dc0f3ab39ec@redhat.com>

openstack-infra/project-config,openstack-infra/project-config