Automatically disable progress for non tty output, i.e. when it's redirected.

Otherwise, a VT100 terminal will soon be assumed.

TEST=touch foo.txt; gclient sync >> foo.txt &; tail -F foo.txt doesn't show progress.
BUG=none

Review URL: http://codereview.chromium.org/3310026

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@59101 0039d316-1c4b-4281-b951-d872f2087c98

gclient.py

@@ -715,7 +715,8 @@ solutions = [
       raise gclient_utils.Error('No solution specified')
     revision_overrides = self._EnforceRevisions()
     pm = None
-    if command == 'update' and not self._options.verbose:
+    # Disable progress for non-tty stdout.
+    if command in ('update', 'revert') and sys.stdout.isatty():
       pm = Progress('Syncing projects', 1)
     work_queue = gclient_utils.ExecutionQueue(self._options.jobs, pm)
     for s in self.dependencies: