Inject concat_basedir fact

This fact has been injected in mutliple spec files. Let's inject it in
a single place so reduce logics in individual spec files.

Depends-on: https://review.opendev.org/c/openstack/puppet-nova/+/876011
Change-Id: Ice931156dfd38b03699c022fe53e3d4898eeb19c

lib/puppet-openstack_spec_helper/defaults.rb

@@ -7,7 +7,8 @@ module OSDefaults
       :os_workers             => 2,
       :os_workers_heat_engine => 2,
       :os_workers_keystone    => 4,
-      :puppetversion          => Puppet.version
+      :puppetversion          => Puppet.version,
+      :concat_basedir         =>  '/dne'
     }.merge(extra_facts)
   end