have toolchain bots use the boards config field

Rather than relying on a global SDK_TEST_BOARDS for all toolchain
configs, use the existing config['boards'] list so we can tweak it
on a per-target basis.

BUG=None
TEST=`cbuildbot chromiumos-sdk` worked
TEST=`cbuildbot mario-paladin` worked
TEST=`cbuildbot refresh-packages` worked

Change-Id: If9984388e1efb782605680f014048e9cca886093
Reviewed-on: https://gerrit.chromium.org/gerrit/37129
Reviewed-by: Brian Harring <ferringb@chromium.org>
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index 8f83a9b..79a3975 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -378,17 +378,18 @@
 
   def RunStages(self):
     """Runs through build process."""
-    self._RunStage(stages.BuildBoardStage)
-
     # TODO(sosa): Split these out into classes.
     if self.build_config['build_type'] == constants.CHROOT_BUILDER_TYPE:
+      self._RunStage(stages.BuildBoardStage, [constants.CHROOT_BUILDER_BOARD])
       self._RunStage(stages.SDKPackageStage)
       self._RunStage(stages.SDKTestStage)
       self._RunStage(stages.UploadPrebuiltsStage,
                      constants.CHROOT_BUILDER_BOARD, None)
     elif self.build_config['build_type'] == constants.REFRESH_PACKAGES_TYPE:
+      self._RunStage(stages.BuildBoardStage)
       self._RunStage(stages.RefreshPackageStatusStage)
     else:
+      self._RunStage(stages.BuildBoardStage)
       self._RunStage(stages.UprevStage)
 
       configs = self.build_config['board_specific_configs']