triggers/gitlab: allow setting the merge request pending build name

Add a "pending-build-name" parameter to control the pendingBuildName XML
attribute which controls the pending build name in the Gitlab merge request.

Change-Id: Iee229a047cbeef6fe842c010feb7963412667066

jenkins_jobs/modules/triggers.py

@@ -1573,6 +1573,7 @@ def gitlab(registry, xml_parent, data):
         (eg. Merge request or Git Push) (default true)
     :arg bool cancel-pending-builds-on-update: Cancel pending merge request
         builds on update (default false)
+    :arg str pending-build-name: Set the pending merge request build name (optional)
     :arg bool add-note-merge-request: Add note with build status on
         merge requests (default true)
     :arg bool add-vote-merge-request: Vote added to note with build status
@@ -1693,17 +1694,19 @@ def gitlab(registry, xml_parent, data):
         ("target-branch-regex", "targetBranchRegex", ""),
         ("secret-token", "secretToken", ""),
     ]
+    helpers.convert_mapping_to_xml(gitlab, data, mapping, fail_required=True)
 
     list_mapping = (
         ("include-branches", "includeBranchesSpec", []),
         ("exclude-branches", "excludeBranchesSpec", []),
     )
-    helpers.convert_mapping_to_xml(gitlab, data, mapping, fail_required=True)
-
     for yaml_name, xml_name, default_val in list_mapping:
         value = ", ".join(data.get(yaml_name, default_val))
         _add_xml(gitlab, xml_name, value)
 
+    optional_mapping = (("pending-build-name", "pendingBuildName", None),)
+    helpers.convert_mapping_to_xml(gitlab, data, optional_mapping, fail_required=False)
+
 
 def gogs(registry, xml_parent, data):
     """yaml: gogs

tests/triggers/fixtures/gitlab004.xml

@@ -24,6 +24,7 @@
       <secretToken/>
       <includeBranchesSpec>master, master2, local-test</includeBranchesSpec>
       <excludeBranchesSpec>broken-test, master-foo</excludeBranchesSpec>
+      <pendingBuildName>test</pendingBuildName>
     </com.dabsquared.gitlabjenkins.GitLabPushTrigger>
   </triggers>
 </project>

tests/triggers/fixtures/gitlab004.yaml

@@ -16,3 +16,4 @@ triggers:
       exclude-branches:
         - 'broken-test'
         - 'master-foo'
+      pending-build-name: 'test'