Fix bf luis:test command failures for corner cases of prebuilt entities

[feich-ms]

Fix #1121. In some corner cases, the predicted entities will not return a standard format, e.g. the prebuilt ordinalV2 entity will return an object value like {offset: 1, relative: current} rather than string or number value, in such case, the entity parsing logic will throw exception caused by non validation. The fix is simple, just add the iterable validation for sub entities value. Test case is also adjusted to test this case.