Fix regression with lost fostered marker on fostered text nodes.

* With recent data-object refactoring, a small oversight setting
  data-parsoid on a span wrapper led to fostered text nodes not
  getting marked as fostered content.

  In turn, this led to selser not protecting edits on pages that
  generated fostered text nodes (fostered elements continued to
  be protected).

* Added a new test to trap these regressions -- but the regressions
  will show as "passing" selser tests (when selser starts agreeing
  with dirty-diffed wt2wt output). For this patch, all selser tests
  get marked as "failing" and are currently blacklisted.

Change-Id: I84e92eb69910fdd19783de61aba37db8b99ec569