Refactor tests to avoid assumptions about serialization implementation

[jacobq]

It wasn't clear to me where the ${modelName}_2 portion of the docId was coming from (this shows up a bunch of places in the test suite, and I was also noticing it in my app). It seems to be from relational-pouch's serialize. If that's the case, doesn't making assumptions about the implementation details of that function make the tests somewhat brittle? (i.e. ember-pouch shouldn't have to care how relational-pouch serializes things)

Perhaps ember-pouch could/should use rel.makeDocID to generate these strings instead?

Admittedly, I haven't done much with PouchDB or relational-pouch before, but it seems to me like this addon accidentally makes use of knowledge of the inner workings of relational-pouch (not just its public API). Are there cases where the API presented by relational-pouch (find, del, save, ...) isn't sufficient and thus we need to directly use PouchDB's API (get, put, bulkDocs, ...)?