unit test: query: runQuery

#### Background
[`runQuery`](https://github.com/influxdata/influxdb/blob/master/ui/src/shared/apis/query.ts#L36-L179) handles executing a query: making a request and processing the response.

Most of the logic of the method is involved in response handling, which are handled by private methods. Testing this method will involve faking a request and triggering a response to cause specific conditions in response and error handlers to be triggered

#### Acceptance Criteria
When looking through the possible code paths, these areas should be covered with tests:

- `processResponse`
- [ ] `processSuccessResponse`
- [ ] `reader.read()`
- [ ] loop with `trimPartialLines()`
- [ ] `processRateLimitResponse`
- `processErrorResponse`
- [ ] parseable error
- [ ] unknown error