ensure we return string on exceptions during form_publishing, closes #285

This reverts commit 43cdc84ccf9264cd89fa55c30d00c0e6b16f018b.
Merge branch 'master' into 285-exceptions-form-publish

* master:
  UK: return appropriate error for corrupted files, closes #416
Merge pull request #430 from onaio/285-exceptions-form-publish

set exceptions as a unicode string during form publishing