build_packages succeeded in building the packages but cros_install_debug_syms failed.

https://cros-goldeneye.corp.google.com/chromeos/healthmonitoring/buildDetails?buildbucketId=8926508421061118656

File "/mnt/host/source/chromite/bin/cros_install_debug_syms", line 169, in <module>
   DoMain()
 File "/mnt/host/source/chromite/bin/cros_install_debug_syms", line 165, in DoMain
   commandline.ScriptWrapperMain(FindTarget)
 File "/mnt/host/source/chromite/lib/commandline.py", line 912, in ScriptWrapperMain
   ret = target(argv[1:])
 File "/mnt/host/source/chromite/scripts/cros_install_debug_syms.py", line 324, in main
   processes=options.jobs)
 File "/mnt/host/source/chromite/lib/parallel.py", line 809, in RunTasksInProcessPool
   queue.put((idx, input_args))
 File "<string>", line 2, in put
 File "/usr/lib64/python2.7/multiprocessing/managers.py", line 758, in _callmethod
   conn.send((self._id, methodname, args, kwds))
cPickle.PicklingError: Can't pickle <class 'portage.dbapi.vartree._owners_db'>: attribute lookup portage.dbapi.vartree._owners_db failed