GC operation might be time consuming and it prevents the other tasks to be executed in WorkQueue (e.g. reviewers plugin cannot add reviewers). Set default and minimum value to 2 so that running GC (either scheduled or on-demand) is not blocking other background tasks. Change-Id: I234e8754f235c1e10837dc98b9c4e3b9568676aa Signed-off-by: Jacek Centkowski <jcentkowski@collab.net>