Calculate version number at initialization instead of in BuildTarget stage

This simplifies the logic for communicating the version number and avoids
the need for queues.

BUG=chromium-os:39767
TEST=--remote, --buildbot --debug, --buildbot --debug --version trybot runs
Change-Id: I0135dd730f88c5a80d497b4963e569ebdde9f32f
Reviewed-on: https://gerrit.chromium.org/gerrit/45271
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: David James <davidjames@chromium.org>
Tested-by: David James <davidjames@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index 7c203fa..47e6b8d 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -401,7 +401,7 @@
       for board in self.build_config['boards']:
         config = configs.get(board, self.build_config)
         archive_stage = self._GetStageInstance(stages.ArchiveStage, board,
-                                               config=config)
+                                               self.release_tag, config=config)
         self.archive_stages[board] = archive_stage
 
       # Set up a process pool to run test/archive stages in the background.
@@ -413,7 +413,7 @@
           archive_stage = self.archive_stages[board]
           config = configs.get(board, self.build_config)
           self._RunStage(stages.BuildTargetStage, board, archive_stage,
-                         self.release_tag, config=config)
+                         config=config)
           self.archive_urls[board] = archive_stage.GetDownloadUrl()
 
           # Kick off task(board) in the background.