GTTF: changes that allow testing CQ locally

This includes the following changes:

1) Use ReadOnlyRietveld from depot_tools (so that it can stay in sync with Rietveld)
2) No longer support --only-issue in dry run mode
3) Fix a unicode bug leading to an exception during testing

I've tested this as "./commit_queue.py --fake --no-try --project chromium"

BUG=291335
[email protected]

Review URL: https://codereview.chromium.org/24303002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/commit-queue@225056 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed