Partial cherry-pick of 6c881c52 from the 2.1 branch

This cherry-picks the utils.FieldSet.Matches changes and the significant
jqueue.py change. These are stable in the 2.1 branch and therefore make
sense to backport to 2.0 (are basically cleanups).

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Olivier Tharan <olive@google.com>