Allow loading additional variables file for site config

It would be useful to allow deployment specific configuration that can
be fed into the project-config deployments so that we can customize
things like host ip without having to change job definitions for each
site.

Also, add a method to display the build log from a failed assertion in
the Ansible test (this was used in the development of the tests for
this change).

Change-Id: I87e8bffc540bcafab543c46244f3d5327b56fcae
Co-Authored-By: James E. Blair <jeblair@redhat.com>
diff --git a/tests/fixtures/config/ansible/variables.yaml b/tests/fixtures/config/ansible/variables.yaml
new file mode 100644
index 0000000..692eb7f
--- /dev/null
+++ b/tests/fixtures/config/ansible/variables.yaml
@@ -0,0 +1 @@
+vartest_site: vartest_site