Suggest --no-thin based on error output

I never remember in the moment how to resolve the occasional "Missing
tree" error. Every time, I have to search and eventually rediscover
https://storyboard.openstack.org/#!/story/1332549 and --no-thin.

Now, on error check for the "Missing tree" message and suggest
--no-thin if it wasn't already enabled.

Change-Id: I7be68812b68f661219a6687fea54c48bc41adac8

git_review/cmd.py

@@ -1866,6 +1866,8 @@ additional information:
     else:
         (status, output) = run_command_status(cmd)
         print(output)
+        if status == 1 and 'Missing tree' in output and not options.no_thin:
+            print('Consider trying again with --no-thin')
 
     if options.finish and not options.dry and status == 0:
         finish_branch(branch)