Add a SignerStage to cbuildbot.

This adds a new stage to cbuildbot that will block until the signer results
are uploaded, and fail the build if they don't all pass.

This stage should be run as a background task, and block until the board
specific push_images command has completed.

BUG=chromium:329397
TEST=Unittests
CQ-DEPEND=CL:183566

Change-Id: I6849109134a3d542602159cf3aeea2d0ce9f58dd
Reviewed-on: https://chromium-review.googlesource.com/182708
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Don Garrett <dgarrett@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index c570c70..862cc99 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -435,6 +435,7 @@
     stage_list += [
         [stages.RetryStage, 1, stages.VMTestStage, board, archive_stage],
         [stages.SignerTestStage, board, archive_stage],
+        [stages.SignerResultsStage, board, archive_stage],
         [stages.UnitTestStage, board],
         [stages.UploadPrebuiltsStage, board, archive_stage],
         [stages.DevInstallerPrebuiltsStage, board, archive_stage],
@@ -1113,6 +1114,9 @@
   group.add_remote_option('--nosdk', action='store_true',
                           default=False,
                           help='Re-create the SDK from scratch.')
+  group.add_remote_option('--nosigner-results', action='store_false',
+                          dest='signer_results', default=True,
+                          help="Don't display signing results.")
   group.add_remote_option('--nosync', action='store_false', dest='sync',
                           default=True, help="Don't sync before building.")
   group.add_remote_option('--notests', action='store_false', dest='tests',