Refresh token flow is not supported by Adobe Analytics V2 APIs under Adobe IO.
In the context of Adobe Analytics, Adobe IO's oAuth authentication should be used by applications that authenticate a human user for the duration of a single session. It is not suitable for use by applications that need "headless" server-to-server, service-token, or long-running authenticaitons.
In Q1 2019 (coming very soon), Analytics will support JWT authentication for situations that require server-to-server, service-token, or other long-running authentications.
We're working to update the Analytics documentation to reflect these specific ways in which the Analytics authentication under Adobe IO differs from the more general Adobe IO authentication mechanisms.