When a playbook fails, don't succeed in the error_block

Make sure that a call into the error_block for "rescue" does not
cause the playbook to be considered a success. This uses the
Ansible fail module to indicate failure.

Change-Id: I07d2f06aa74cfe9dd0f7a1c3a64d4e51290bd570
Partial-Story: #2000619
diff --git a/zuul/launcher/ansiblelaunchserver.py b/zuul/launcher/ansiblelaunchserver.py
index 5ecc954..43b2c4e 100644
--- a/zuul/launcher/ansiblelaunchserver.py
+++ b/zuul/launcher/ansiblelaunchserver.py
@@ -876,6 +876,7 @@
 
             task = dict(zuul_log=dict(msg="Job complete, result: FAILURE"))
             error_block.append(task)
+            error_block.append(dict(fail=dict(msg='FAILURE')))
 
             play = dict(hosts='node', name='Job body',
                         tasks=tasks)