LBCORE 907: implement a slot that handles Gaudi gitlab merge requests

Marco Clemencic requested to merge clemenci/LbNightlyTools:LBCORE-907 into master
  • modified the slot configuration retrieval to use also configs/ as source
  • extended git checkout to handle merges from extra repositories
  • extended Gaudi checkout to use the special version mr## to select a merge request from gitlab

The Jenkins checkout script expects the optional special variable LBN_GAUDI_MR to flag a build as a merge request, in which case it expects either the environment variable GITLAB_TOKEN or the file ~/private/gitlab_token.txt.

Merge request reports