cros_set_lsb_release: write out new CHROMEOS_RELEASE_KEYSET field

We want to separate this info out of CHROMEOS_RELEASE_BOARD, so
start stamping it in images so consumers can start migrating.

BUG=chromium:443736
TEST=unittests pass

Change-Id: I9ec0f9fb831f009a209adf15d5264551c16b2ce1
Reviewed-on: https://chromium-review.googlesource.com/1217266
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Jason Clinton <jclinton@chromium.org>
diff --git a/scripts/cros_set_lsb_release.py b/scripts/cros_set_lsb_release.py
index ba20cf6..ffcb660 100644
--- a/scripts/cros_set_lsb_release.py
+++ b/scripts/cros_set_lsb_release.py
@@ -30,6 +30,7 @@
 # CHROMEOS_RELEASE_PATCH_NUMBER is the patch number for the current branch.
 # CHROMEOS_RELEASE_TRACK and CHROMEOS_RELEASE_VERSION are used by the software
 #   update service.
+# CHROMEOS_RELEASE_KEYSET is the named of the keyset used to sign this build.
 # TODO(skrul):  Remove GOOGLE_RELEASE once Chromium is updated to look at
 #   CHROMEOS_RELEASE_VERSION for UserAgent data.
 LSB_KEY_NAME = 'CHROMEOS_RELEASE_NAME'
@@ -39,6 +40,7 @@
 LSB_KEY_BUILD_TYPE = 'CHROMEOS_RELEASE_BUILD_TYPE'
 LSB_KEY_DESCRIPTION = 'CHROMEOS_RELEASE_DESCRIPTION'
 LSB_KEY_BOARD = 'CHROMEOS_RELEASE_BOARD'
+LSB_KEY_KEYSET = 'CHROMEOS_RELEASE_KEYSET'
 LSB_KEY_MODELS = 'CHROMEOS_RELEASE_MODELS'
 LSB_KEY_UNIBUILD = 'CHROMEOS_RELEASE_UNIBUILD'
 LSB_KEY_BRANCH_NUMBER = 'CHROMEOS_RELEASE_BRANCH_NUMBER'
@@ -77,6 +79,8 @@
   parser.add_argument('--official', action='store_true',
                       help='Whether or not to populate with fields for an '
                       'official image.')
+  parser.add_argument('--keyset',
+                      help='The keyset name used to sign this image.')
   parser.add_argument('--buildbot_build', default='N/A',
                       help='The build number, for use with the continuous '
                       'builder.')
@@ -151,6 +155,11 @@
         LSB_KEY_BUILDER_PATH: opts.builder_path,
     })
 
+  if opts.keyset is not None:
+    fields.update({
+        LSB_KEY_BOARD: opts.keyset,
+    })
+
   board_and_models = opts.board
   if opts.models:
     board_and_models += '-unibuild (%s)' % opts.models