Added fatal error checks in format test suite
Added fatal error checks in format test suite

refs https://github.com/TryGhost/Toolbox/issues/241

- The change introduces a new concept of checking for "fatal" type of errors in the output.
- The checks have been added for v4 and v5 suites as those are the ones that are most likely to get changes and will be maintained in the future. The rest might get similar checks in the future if there's such a need

TryGhost/gscan