Add in option to always disable gsutil version check

In theory this shouldn't fire if gsutil is running without a tty (ie, in a subprocess).
In practice we're still seeing processes hang because it still thinks it's in a tty
This should in theory disable the prompt for good

BUG=577325,576979

Review URL: https://codereview.chromium.org/1587793002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@299714 0039d316-1c4b-4281-b951-d872f2087c98

gsutil.py

@@ -125,7 +125,8 @@ def run_gsutil(force_version, fallback, target, args, clean=False):
     gsutil_bin = ensure_gsutil(force_version, target, clean)
   else:
     gsutil_bin = fallback
-  cmd = [sys.executable, gsutil_bin] + args
+  disable_update = ['-o', 'GSUtil:software_update_check_period=0']
+  cmd = [sys.executable, gsutil_bin] + disable_update + args
   return subprocess.call(cmd)