Gitlab-plugin: Pipeline ref name incorrect for tag push events

[gempain]

Issue

Context

• Gitlab plugin version: 1.5.2
• Gitlab version: 10.2.2
• Jenkins version: 2.73.3
• Job type: Freestyle

Problem description

When a build is triggered by a tag push event, the CI job branch name that appears in Gitlab CI is wrong:

I would expect refs/tags/<tag-name> to be <tag-name>.

This has two consequences:

• it conflicts with Gitlab CI native behavior: for a tagged commit, CI jobs use the tag name as job branch name:
  
• when you click the title, it should take you to <gitlab-url>/<repo-path>/commits/<tag-name>, but it actually takes you to <gitlab-url>/<repo-path>/commits/refs/tags/<tag-name>, which returns a 404.

Edit: here is an even better example:

[omehegan]

I suspect this is an issue with how we return data to GitLab for builds triggered by tags. Needs investigation.

[omehegan]

Released in version 1.5.7.

[rililinx]

Hi. I faced with it in:
gitlab plugin version: 1.5.10
Gitlab version: 11.2.3
Jenkins version: 2.138.2
Job type: Freestyle