cubicweb #689182 Improve the error message for StaticVocabularyConstraint [resolved]

Currently when we set a value for an attribute (for which a static vocabulary is defined) which is not in the possible values, we have an error like this:

value in (u'abc', u'def', u'ghi') constraint failed for value u'truc'

which is not very clear.

A message like this one is more appropriate:

invalid value for u'truc', value must be one of these (u'abc', u'def', u'ghi')
done in3.8.1
load left0.000
closed by<not specified>