Reland "Removes attempts and build numbers from imaging artifacts.""

See bug.  This removes the attempt and build numbers for
versioned builds by refactoring the versioning logic and
slightly tweaking the interface to build_image.

Build versions for versioned builds will look like:
R19-2048.0.0

Non versoined builds will keep the same naming scheme i.e.
for x86-generic-full etc.

Originally reviewed in: I6bab04211e2217a3705d9e77532984a741acef97

BUG=chromium-os:29077
TEST=Unittests + previously run through canaries

Change-Id: I3e8513c586d7e7353a12191e55e10fd43baf7ee0
Reviewed-on: https://gerrit.chromium.org/gerrit/20109
Commit-Ready: Chris Sosa <sosa@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Tested-by: Chris Sosa <sosa@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index e7c4920..d46da91 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -388,7 +388,7 @@
           archive_stage = self.archive_stages[board]
           config = configs.get(board, self.build_config)
           self._RunStage(stages.BuildTargetStage, board, archive_stage,
-                         config=config)
+                         self.release_tag, config=config)
           self.archive_urls[board] = archive_stage.GetDownloadUrl()
 
           # Kick off task(board) in the background.