Add support for zulip notifications.

Post-build action to notify build status your company's zulip.com
account via Zulip notifications. It uses  Humbug Plugin as detailed
here https://zulip.com/integrations/#jenkins
The notifications settings are needed to be done globally in jenkins
so this publisher only lets to add the action of zulip notifications
to your job with no parameters required, similar to blame-upstream
https://docs.openstack.org/infra/jenkins-job-builder/publishers.html#publishers.blame-upstream

Change-Id: Idea0dc0b1dc36b405171a40e6ce81f5d521e794a

jenkins_jobs/modules/publishers.py

@@ -3389,6 +3389,20 @@ def github_notifier(parser, xml_parent, data):
                    'com.cloudbees.jenkins.GitHubCommitNotifier')
 
 
+def zulip(parser, xml_parent, data):
+    """yaml: zulip
+    Set build status on zulip.
+    Requires the Jenkins :jenkins-wiki:`Humbug Plugin <Humbug+Plugin>`.
+
+    Example:
+
+    .. literalinclude:: /../../tests/publishers/fixtures/zulip.yaml
+       :language: yaml
+    """
+    XML.SubElement(xml_parent,
+                   'hudson.plugins.humbug.HumbugNotifier')
+
+
 def build_publisher(parser, xml_parent, data):
     """yaml: build-publisher
     This plugin allows records from one Jenkins to be published

setup.cfg

@@ -213,6 +213,7 @@ jenkins_jobs.publishers =
     workspace-cleanup=jenkins_jobs.modules.publishers:workspace_cleanup
     xml-summary=jenkins_jobs.modules.publishers:xml_summary
     xunit=jenkins_jobs.modules.publishers:xunit
+    zulip=jenkins_jobs.modules.publishers:zulip
 jenkins_jobs.scm =
     git=jenkins_jobs.modules.scm:git
     hg=jenkins_jobs.modules.scm:hg

tests/publishers/fixtures/zulip.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<project>
+  <publishers>
+    <hudson.plugins.humbug.HumbugNotifier/>
+  </publishers>
+</project>

tests/publishers/fixtures/zulip.yaml

@@ -0,0 +1,2 @@
+publishers:
+  - zulip