gclient-sync + git-cache are racy because if two different DEPS files
dependent on the same repo URL, even if depsed to different checkout
dirs, they use same git cache dir. If both checkout dirs are synced at
the same time, one of them cannot acquire a lock.

This is a cheap solution to change --lock_timeout option default value
from 0 to 5m.

R=hinoka@chromium.org
BUG=593468

Review URL: https://codereview.chromium.org/1785083005

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@299386 0039d316-1c4b-4281-b951-d872f2087c98