yocto2.groovy: add timestamper
yocto2.groovy: add timestamper

Timestamper plugin call was added for most time consuming
pieces of pipeline to follow the proccess of building

Signed-off-by: Dmytro Iurchuk <16ba42971a6f2e7a0d103a9f9b92eff4116e1776@luxoft.com>

Pelagicore/pelux-manifests,sashko/pelux-manifests