refactor: migrate

[jannyHou]

Description

connect to https://github.com/strongloop/loopback-connector-cloudant/pull/225.

To support partitioned index in cloudant connector, I refactored some inner functions into private functions.

The new cloudant driver supports {partitioned: true/false} as a property when create the index, while nano hasn't yet(and treat partitioned as an invalid property), that's why the index object generation functions in the couchdb connector still takes in fields only, instead of an object with property fields, partitioned.

Related issues

• connect to strongloop/loopback-connector-cloudant#225

Checklist

• [x] New tests added or existing tests modified to cover all changes
• [x] Code conforms with the style guide

[jannyHou]

@slnode test please

[rmg]

@slnode test please

[jannyHou]

@slnode test please