[MODEL] Fix wrong retrieval of records corresponding to indexed documents when querying multiple models

[miguelff]

This PR fixes #369

• The first commit adds a fix for a regression introduced in Force no_timeout in mongoid adapter #335, to depart from a green build
• The second commit includes:
  • A refactor over a case/when statement, as for objects. case/when only matches the branches in which === returns true. i.e. an object that is instance of a class. But if the object is a class itself, or a module like the adapters, it won't enter any of the when branches.
  • Taking back the call to compact over the collection of records, because as per eventual consistency, ES can return some results, which corresponding records no longer exist. As a consequence, calling records would return an array with positions including nil.
  • An integration test checking the correctness of the two points above.
• The third commit cleans up a bit the integration tests for multiple model.

[karmi]

@miguelff Thanks, merged!