BuildPackages: Add a flag to gate updating the metadata.

The flag will be set so that firmware version information is written to
the metadata only once per build.

BUG=chromium:404354
TEST=Ran a tryjob on lumpy-incremental-paladin. Ran run_tests.

Change-Id: Iee4077c52955d09805da41e2304cc73bc5e0b6ab
Reviewed-on: https://chromium-review.googlesource.com/213009
Reviewed-by: Gabe Black <gabeblack@chromium.org>
Commit-Queue: Gabe Black <gabeblack@chromium.org>
Tested-by: Gabe Black <gabeblack@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index 00c62dc..3ab8d75 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -520,7 +520,8 @@
 
     if config.build_packages_in_background:
       self._RunStage(build_stages.BuildPackagesStage, board,
-                     builder_run=builder_run, afdo_use=config.afdo_use)
+                     update_metadata=True, builder_run=builder_run,
+                     afdo_use=config.afdo_use)
 
     if builder_run.config.compilecheck or builder_run.options.compilecheck:
       self._RunStage(test_stages.UnitTestStage, board,
@@ -657,7 +658,8 @@
           elif builder_run.config.afdo_use:
             kwargs['afdo_use'] = True
 
-          self._RunStage(build_stages.BuildPackagesStage, board, **kwargs)
+          self._RunStage(build_stages.BuildPackagesStage, board,
+                         update_metadata=True, **kwargs)
 
           if (builder_run.config.afdo_generate_min and
               afdo.CanGenerateAFDOData(board)):