git cl: suggest running git cl creds-check after git push failures.

R=sergiyb@chromium.org
BUG=708785

Change-Id: Ib29be04cda18b0b1187893e555a4c5a7ea753e6e
Reviewed-on: https://chromium-review.googlesource.com/472866
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>

git_cl.py

@@ -2984,7 +2984,11 @@ class _GerritChangelistImpl(_ChangelistCodereviewBase):
           filter_fn=lambda _: sys.stdout.flush())
     except subprocess2.CalledProcessError:
       DieWithError('Failed to create a change. Please examine output above '
-                   'for the reason of the failure. ', change_desc)
+                   'for the reason of the failure.\n'
+                   'Hint: run command below to diangose common Git/Gerrit '
+                   'credential problems:\n'
+                   '  git cl creds-check\n',
+                   change_desc)
 
     if options.squash:
       regex = re.compile(r'remote:\s+https?://[\w\-\.\/]*/(\d+)\s.*')
@@ -5040,7 +5044,10 @@ def PushToGitWithAutoRebase(remote, branch, original_description,
       break
     if IsFatalPushFailure(out):
       print('Fatal push error. Make sure your .netrc credentials and git '
-            'user.email are correct and you have push access to the repo.')
+            'user.email are correct and you have push access to the repo.\n'
+            'Hint: run command below to diangose common Git/Gerrit credential '
+            'problems:\n'
+            '  git cl creds-check\n')
       break
   return code