Fixes an ImportError exception because some bots do not have the multiprocessing library
Fixes an ImportError exception because some bots do not have the multiprocessing library

BUG= None
TEST= Ran build_tools/buildbot_run.py manually and verified that it works.

Review URL: http://codereview.chromium.org/6673091

git-svn-id: e22621a84199d42b34715cdc089545aeedbbf23f@775 050acbb0-2703-11df-ab0a-9f3f633ae91d

sbc100/nativeclient-sdk,sbc100/nativeclient-sdk,sbc100/nativeclient-sdk,sbc100/nativeclient-sdk,sbc100/nativeclient-sdk,sbc100/nativeclient-sdk,sbc100/nativeclient-sdk