Make gclient fetch git repos recursively. This is needed when adding a git repo through DEPS. If that repo has submodules, we need to fetch them or else the repo won't be complete.

Review URL: https://chromiumcodereview.appspot.com/12620024

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@189026 0039d316-1c4b-4281-b951-d872f2087c98