This fixes GClientSmokeBoth.testMultiSolutionsJobs flakiness by having
consistent ordering.

Now no out of thread modification is ever done, which result in much saner code.

R=dpranke@chromium.org
BUG=60725
TEST=tested manually with gclient sync --jobs 100 on chrome and with
gclient_smotetest.py


Review URL: http://codereview.chromium.org/8174014

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@104920 0039d316-1c4b-4281-b951-d872f2087c98