[BUGFIX] include may not have a .relation and just be a { [modelName]: true } sometimes

[abhilashmurthy]

Used to fail when my model has a default scope in its model.json

scope: {
  include: ['model1', 'model2']
}

and I make a filter REST API call with
/api/model?include=model3

Turns out the requested include was never included in the serialised result because

1. isLoopbackInclude checked for an incomplete condition, which overrode isJSONAPIInclude -> added ctx.args.filter.include to make it correct
2. setRequestedInclude did not account for object of type { [modelName]: true } -> made it do so

[coveralls]

Coverage remained the same at 94.554% when pulling d28e324 on abhilashmurthy:fix-requested-include-pojo into a7083aa on digitalsadhu:master.