Fix for authenticating to internal repos

Last patch (https://codereview.chromium.org/313933005/) forgot to take into account using a boto file (setting boto to os.devnull
means connect unauthenticated, setting it to None will allow it to do the default
behavior)

This patch will always use a boto file, which should be fine.

BUG=261741

Review URL: https://codereview.chromium.org/314203002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@275230 0039d316-1c4b-4281-b951-d872f2087c98

git_cache.py

@@ -252,8 +252,7 @@ class Mirror(object):
       python_fallback = True
 
     gs_folder = 'gs://%s/%s' % (self.bootstrap_bucket, self.basedir)
-    gsutil = Gsutil(
-        self.gsutil_exe, boto_path=os.devnull, bypass_prodaccess=True)
+    gsutil = Gsutil(self.gsutil_exe, bypass_prodaccess=True)
     # Get the most recent version of the zipfile.
     _, ls_out, _ = gsutil.check_call('ls', gs_folder)
     ls_out_sorted = sorted(ls_out.splitlines())