Dev Install: Add support for --yes option to assume y's to all prompts.

Also some fixes to gmerge workflow to allow easy integration testing.

BUG=chromium-os:12388, chromium-os:37901
TEST=Ran it with devmode-test

Change-Id: If511a65fb81fb2ed3d425005490efc9353283274
Reviewed-on: https://gerrit.chromium.org/gerrit/44763
Commit-Queue: Chris Sosa <sosa@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Tested-by: Chris Sosa <sosa@chromium.org>
diff --git a/builder.py b/builder.py
index 0530136..c24422a 100644
--- a/builder.py
+++ b/builder.py
@@ -200,8 +200,8 @@
       _AppendStrToEnvVar(env_copy, 'FEATURES', additional_args['features'])
 
     try:
-      if (self._ShouldBeWorkedOn(board, pkg) and
-          not additional_args.get('accept_stable')):
+      if (not additional_args.get('accept_stable')
+          and self._ShouldBeWorkedOn(board, pkg)):
         return self.SetError(
             'Package is not cros_workon\'d on the devserver machine.\n'
             'Either start working on the package or pass --accept_stable '