Cleanup UI properly after error

I observed that after a failure, the UI did not clean itself up
properly. Subsequent exports worked, but would continue to display the
earlier failure message.

I reworked the displayManager to be a little simpler as well.
Merge pull request #1621 from steventlamb/bug/export_ui_cleanup

Cleanup UI properly after error
Don't hard code instance names in tests
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Merge pull request #1623 from steventlamb/topic/hidden_comment_ui

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