Change validation error message to include dataPath and subErrors

Validation errors are not expressive and doesn't print the subErrors.  

Currently validation errors show:
```
$ ./node_modules/.bin/swaggerize --api config/api.json --handlers resources/handlers --models resources/models --tests tests
Data does not match any schemas from "oneOf"
```

This adds additional context (dataPath) and prints subErrors:
```
 ./node_modules/.bin/swaggerize --api config/api.json --handlers resources/handlers --models resources/models --tests tests
/models/Item/properties/tags/items: ValidationError: Data does not match any schemas from "oneOf"
/models/Item/properties/tags/items: ValidationError: Missing required property: $ref
/models/Item/properties/tags/items/description: ValidationError: Additional properties not allowed
```