Don't show error operations after a successful land operation
Ref T182. When viewing a revision, if there are several error operations and then a success operation, we currently show the last error. This is misleading.
Instead, don't show anything if there's a success (this may require tuning eventually if you can land multiple times onto different branches or whatever, but should be reasonable for now).
Also make the table a little nicer, particularly for merge failure output.
Reviewers: chad, Mnkras
Reviewed By: Mnkras
Maniphest Tasks: T182
Differential Revision: https://secure.phabricator.com/D14348