allows one to run the presubmit script without
submitting locally (alternative would be to make 
this a warning I guess).

Also, pass option.verbose through to DoGetTrySlaves()
so it will log which PRESUBMIT files are taking part
in the decision.

BUG=

Review URL: https://chromiumcodereview.appspot.com/10915072

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@154838 0039d316-1c4b-4281-b951-d872f2087c98