Fix issue with stale cache from bad builds.

bin/cbuildbot.py

Index: bin/cbuildbot.py
diff --git a/bin/cbuildbot.py b/bin/cbuildbot.py
index 37a8b6e2691943905479a02594c9e510f9bed561..f000a576c39a57d075e6e97cc1006406d78d844c 100755
--- a/bin/cbuildbot.py
+++ b/bin/cbuildbot.py
@@ -345,6 +345,14 @@ def _UprevCleanup(buildroot, error_ok=False):
               '--tracking_branch="cros/master"', 'clean'],
              cwd=cwd, error_ok=error_ok)
 
+  workon_packages = RunCommand(['./cros_workon', 'list'],
+                               enter_chroot=True, cwd=cwd, error_ok=error_ok,
+                               redirect_stdout=True)
+  if workon_packages:
+    Info('Cleaning up workon packages %s' % workon_packages)
+    RunCommand(['./cros_workon', 'stop'] + workon_packages.split(),
+               enter_chroot=True, cwd=cwd, error_ok=False)
+
 
 def _UprevPush(buildroot):
   """Pushes uprev changes to the main line."""
@@ -439,7 +447,6 @@ def main():
         # Master bot needs to check if the other slaves completed.
         if cbuildbot_comm.HaveSlavesCompleted(config):
           _UprevPush(buildroot)
-          _UprevCleanup(buildroot)
         else:
           # At least one of the slaves failed or we timed out.
           _UprevCleanup(buildroot)
@@ -449,7 +456,7 @@ def main():
         if buildconfig['important']:
           cbuildbot_comm.PublishStatus(cbuildbot_comm.STATUS_BUILD_COMPLETE)
 
-        _UprevCleanup(buildroot)
+      _UprevCleanup(buildroot)
   except:
     # Send failure to master bot.
     if not buildconfig['master'] and buildconfig['important']: