Update gradle to build with JenkinsPipelineUnit v1.2

[sofiia-kalinina]

Background

Upgrade JenkinsPipelineUnit to v1.2 (see changelog: https://github.com/jenkinsci/JenkinsPipelineUnit/releases/tag/v1.2)

Task description

Edit build.gradle accordingly.

Acceptance criteria

Pipeliner can be built with new gradle build settings successfully.

Acting on Behalf of MBition GmbH

https://github.com/Daimler/daimler-foss/blob/master/LEGAL_IMPRINT.md