Report the expected error indicated by the "negative" frontmatter when it isn't thrown

[goyakin]

Currently, when the expected error indicated by the negative frontmatter isn't thrown, the test harness outputs:

not ok 788 Negative frontmatter test
  ---
    file: |
      c:/src/test262/test/annexB/test.js

However, this doesn't include any information about what the expected outcome is.

This change updates the harness to include this information and output the following instead:

not ok 788 Negative frontmatter test
  ---
    file:         |
      c:/src/test262/test/annexB/test.js
    errorName:    Error Expected
    errorMessage: 'ExpectedError' is expected, but was not thrown