SDK: Create simple test for /stake/delegators/{delegatorAddr}

[NodeGuy]

We're working on improving the performance of /stake/delegators/{delegatorAddr} in #1133.

To support this work we need a simple unit test. Currently there is a test called TestBonding which is 84 lines of code and very complex. We need a test that:

• is simple
• creates its own node and Gaia Lite server
• creates a state of one account delegating to another, nothing else
• creates the state using the Go API, not REST calls
• creates a deterministic state that's the same in every test, including the keys/addresses of both accounts
• located in x/stake/client/rest (e.g., rest_test.go, near the code it's testing)

[faboweb]

I would advice defering any tests like this, until the SDK team has delivered a framework for testing the enables us to easyly do all those things. We can get on their nerves about this, but I don't think we should be developing this.

[faboweb]

Very nicely written issue btw. :) 👍

[NodeGuy]

Moved to cosmos/cosmos-sdk#2307.