Update student training messaging in authoring.

[ORA-731](https://openedx.atlassian.net/browse/ORA-731)

This reverts the change I made earlier this week to wrap all server-side student training errors as "Student training example option does not match the rubric."  This message is confusing when validation fails because a criterion has 0 options.

@stephensanchez 
Sounds reasonable to me.


On Thu, Aug 7, 2014 at 9:42 AM, Will Daly <notifications@github.com> wrote:

> In openassessment/xblock/validation.py:
>
> > @@ -295,7 +295,7 @@ def validate_assessment_examples(rubric_dict, assessments, _):
> >              # examples against the rubric.
> >              errors = validate_training_examples(rubric_dict, examples)
> >              if errors:
> > -                return False, _(u"Student training example option does not match the rubric.")
> > +                return False, "; ".join(errors)
>
> The Studio validation error box doesn't show newlines correctly. Assuming
> that client-side validation is working correctly, we shouldn't have
> multiple errors returned from the API at all, so in most cases it will just
> display the single error message.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/edx/edx-ora2/pull/601/files#r15935372>.
>