sequencer: Simplify error message generation (#1537)
sequencer: Simplify error message generation (#1537)


AlCutter/trillian,daviddrysdale/trillian,daviddrysdale/trillian,google/trillian,Martin2112/trillian,Martin2112/trillian,Martin2112/trillian,gdbelvin/trillian,RJPercival/trillian,daviddrysdale/trillian,gdbelvin/trillian,gdbelvin/trillian,AlCutter/trillian,RJPercival/trillian,google/trillian