git cl: suggest git cl creds-check if Gerrit API returns 401.

R=sergiyb@chromium.org
BUG=708785

Change-Id: Id25d3ef9a1449a0c259ed48b782e1b766e1a5fc9
Reviewed-on: https://chromium-review.googlesource.com/472906
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>

gerrit_util.py

@@ -368,6 +368,9 @@ def ReadHttpResponse(conn, expect_status=200, ignore_404=True):
   if ignore_404 and response.status == 404:
     return StringIO()
   if response.status != expect_status:
+    if response.status in (401, 403):
+      print('Your Gerrit credentials might be misconfigured. Try: \n'
+            '  git cl creds-check')
     reason = '%s: %s' % (response.reason, contents)
     raise GerritError(response.status, reason)
   return StringIO(contents)