Harmonize testing of device registry RPCs

[johanstokking]

Summary:

Harmonize testing of the RPC device registries.

Why do we need this?

For code quality of the open source project and a consistent way of testing.

What is already there? What do you see now?

1. Join Server tests have been rewritten recently, has full test coverage, is readable and can be further extended
2. Network Server tests have been rewritten recently in the style we want to follow.
3. Application Server tests starts up the AS component and uses an RPC client

What is missing? What do you want to see?

1. NS tests are okay. This one serves as a reference
2. AS tests should be like NS.
3. JS tests are okay, but ideally they should be more consistent with NS, if possible.

How do you propose to implement this?

Use the same mechanism. Note that there are minor differences;

• JS uses JoinEUI and DevEUI, while AS and NS use identifiers
• JS registry has a read/write keys, which doesn't exist in NS and AS. That saves test cases

---

Original issue: https://github.com/TheThingsIndustries/lorawan-stack/issues/1459 by @johanstokking

[johanstokking]

Closed by #177