Misleading message "No Gitlab connection configured"

## Issue

Job console logs contain messages "No Gitlab connection configured", while build statuses are successfully reported.

### Context
- **Gitlab plugin version**: 1.5.5
- **Gitlab version**: 10.7.3
- **Jenkins version**: 2.107.2
- **Job type**: Matrix Job/

### Problem description

I've got a matrix job, that is triggered by the Gitlab plugin through webhooks.

Job configuration contains configured "Gitlab connection" in General settings and 3 postbuild actions: "Add note with build status on Gitlab Merge requests", "Add vote for build status for Gitlab Merge requests" and "Publish build status to Gitlab commit".

It also contains a secret token in the advanced settings for Build triggers, and this token is entered in the settings of the Gitlab project.

Configured build trigger is the only "Build when a change is pushed to GitLab. GitLab CI Service URL: "

Console output contains 4 messages "No GitLab connection configured", one after git checkout and before build start, and 3 more in the end of the log.

The respective merge request in Gitlab contains messages like

"Administrator @root commented about an hour ago

:white_check_mark: Jenkins Build SUCCESS

Results available at: Jenkins matrix_job #66 "

that suggests, that build statuses are actually reported