cbuildbot: split debug symbols into a dedicated stage

There's no difference from the previous version.  The hangs experienced
before are not reproducible, and the latest chromite code has better
checks to prevent it from happening.  So we're going to try it in the
CQ and see if we can figure it out if it does fail again.

This pulls all the debug symbol logic out of the Archive stage and into
a stage all by itself.  With the semi-recent changes, these tools have
gotten a bit verbose, so we want to separate them out.

In the future, we'll do more retooling here which will require more code
which will be nicer if it's all in a stage by itself.

This is all mechanical at this point.

BUG=None
TEST=`./buildbot/run_tests` passes

Change-Id: I93992e79ff6094b41d4495d8a8c313f2c35ab695
Reviewed-on: https://chromium-review.googlesource.com/176972
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Matt Tennant <mtennant@chromium.org>
Reviewed-by: David James <davidjames@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index edebd33..0396885 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -425,6 +425,11 @@
                      builder_run=builder_run)
       return
 
+    # While this stage list is run in parallel, the order here dictates the
+    # order that things will be shown in the log.  So group things together
+    # that make sense when read in order.  Also keep in mind that, since we
+    # gather output manually, early slow stages will prevent any output from
+    # later stages showing up until it finishes.
     stage_list = []
     if builder_run.options.chrome_sdk and config.chrome_sdk:
       stage_list.append([stages.ChromeSDKStage, board, archive_stage])
@@ -433,7 +438,8 @@
         [stages.SignerTestStage, board, archive_stage],
         [stages.UnitTestStage, board],
         [stages.UploadPrebuiltsStage, board, archive_stage],
-        [stages.DevInstallerPrebuiltsStage, board, archive_stage]
+        [stages.DevInstallerPrebuiltsStage, board, archive_stage],
+        [stages.DebugSymbolsStage, board, archive_stage],
     ]
 
     # We can not run hw tests without archiving the payloads.