Add change message to Zuul vars in inventory

Having the change message available via the Zuul vars simplifies cases
where a job e.g. needs to update a GitHub/Jira/... ticket.

Those ticket numbers are usually referenced in the commit/PR message.

This avoids having to deal with secrets etc. to get this information
'out-of-band'.

Change-Id: Ib88db7f724dadfb8a4f86e76692f3e1c2c63a258

doc/source/user/jobs.rst

@@ -525,6 +525,10 @@ are available:
       E.g., `https://review.example.org/#/c/123456/` or
       `https://github.com/example/example/pull/1234`.
 
+   .. var:: message
+
+      The commit or pull request message of the change.
+
 Branch Items
 ~~~~~~~~~~~~
 

tests/unit/test_inventory.py

@@ -60,6 +60,7 @@ class TestInventory(TestInventoryBase):
         self.assertIn('src_root', z_vars['executor'])
         self.assertIn('job', z_vars)
         self.assertEqual(z_vars['job'], 'single-inventory')
+        self.assertEqual(z_vars['message'], 'A')
 
         self.executor_server.release()
         self.waitUntilSettled()

zuul/executor/client.py

@@ -175,6 +175,8 @@ class ExecutorClient(object):
             zuul_params['change_url'] = item.change.url
         if hasattr(item.change, 'patchset'):
             zuul_params['patchset'] = str(item.change.patchset)
+        if hasattr(item.change, 'message'):
+            zuul_params['message'] = item.change.message
         if (hasattr(item.change, 'oldrev') and item.change.oldrev
             and item.change.oldrev != '0' * 40):
             zuul_params['oldrev'] = item.change.oldrev