T50900: Add mw:Error + error info to data-mw for missing imgs

* Updated parser tests (with bad/missing images) to use the new
  HTML output.

* Since I added separate html/parsoid sections for all the bad image
  tests, they all pass wt2html now (where they failed previously).

* The bad image parser tests will fail till bug 73581 is handled.

Change-Id: I028f36e60c6ff7800770b9c69a7277652ea0b8d7
Merge "T50900: Add mw:Error + error info to data-mw for missing imgs"