Refactor Jenkins Pipeline

[Jotschi]

1. Allocate a few nodes
2. Distribute jobs to the set of allocated nodes

• Job: https://ci.gentics.com/view/Mesh/job/mesh/job/dev-ci-new/
• Branch: https://github.com/gentics/mesh/tree/dev-ci-new
• PR: https://github.com/gentics/mesh/pull/751

[Jotschi]

Done