Merge branch 'fix_jira_shortterm' into 'master'

Do not call API if there is no API URL

Fixes #5878 

CE users may not be interested in the new JIRA features. In this case,
we should detect they haven't set an API URL and fallback to the
behavior pre-8.3. This patch does that very easily.

There are planned improvements to JIRA in future releases such as
gitlab-org/gitlab-ce#5541 which will make this more configurable.

See merge request !2341

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.3.3 (unreleased)
+  - Preserve CE behavior with JIRA integration by only calling API if URL is set
   - Get "Merge when build succeeds" to work when commits were pushed to MR target branch while builds were running
   - Suppress e-mails on failed builds if allow_failure is set (Stan Hu)
   - Fix project transfer e-mail sending incorrect paths in e-mail notification (Stan Hu)

app/models/project_services/jira_service.rb

@@ -120,6 +120,7 @@ class JiraService < IssueTrackerService
   end
 
   def test_settings
+    return unless api_url.present?
     result = JiraService.get(
       jira_api_test_url,
       headers: {
@@ -217,6 +218,7 @@ class JiraService < IssueTrackerService
   end
 
   def send_message(url, message)
+    return unless api_url.present?
     result = JiraService.post(
       url,
       body: message,
@@ -242,6 +244,7 @@ class JiraService < IssueTrackerService
   end
 
   def existing_comment?(issue_name, new_comment)
+    return unless api_url.present?
     result = JiraService.get(
       comment_url(issue_name),
       headers: {