workflows: disable arXiv updates

* The merging of arXiv records is not stable enough, so we
  temporarily disable it.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
fabfile: backend nodes and bibsched tasks

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
fabfile: fix sync command

* The sync command now excludes folders properly.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>