Put Zuul vars in an ansible vars file

This adds a vars file for use by ansible playbooks with all vars
scoped under 'zuul'.  The existing environment variables will be
moved into this section in a later change.  Currently, the only
supplied variable is 'uuid' for use in a test.

Also, add a test-specific vars entry (zuul._test) so that we can
pass information such as the test chroot into playbooks used in
our tests.  This is used by a test to set a flag file inside of
the test chroot to verify that the ansible playbook in a job
actually ran and did something.

Change-Id: Ie5d950d051accad4ec9dc90a9e1b01b3095a1e5c
Co-Authored-By: Monty Taylor <mordred@inaugust.com>
diff --git a/tests/unit/test_v3.py b/tests/unit/test_v3.py
index 96f24a1..9034bf7 100644
--- a/tests/unit/test_v3.py
+++ b/tests/unit/test_v3.py
@@ -15,6 +15,7 @@
 # under the License.
 
 import logging
+import os
 import textwrap
 
 from tests.base import AnsibleZuulTestCase
@@ -129,5 +130,7 @@
         A = self.fake_gerrit.addFakeChange('org/project', 'master', 'A')
         self.fake_gerrit.addEvent(A.getPatchsetCreatedEvent(1))
         self.waitUntilSettled()
-        self.assertEqual(self.getJobFromHistory('python27').result,
-                         'SUCCESS')
+        build = self.getJobFromHistory('python27')
+        self.assertEqual(build.result, 'SUCCESS')
+        flag_path = os.path.join(self.test_root, build.uuid + '.flag')
+        self.assertTrue(os.path.exists(flag_path))