Fix: GRPCIndex.query future result type

[yorickvP]

This was missing a parse_query_response call, causing the result to be the raw Message.

Problem

GRPCIndex.query was returning a raw Message when using async_req. This change fixes that.

Solution

Set a result_transformer on the future to parse it.

Type of Change

This is somewhat breaking because anyone affected was likely working around it.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Infrastructure change (CI configs, etc)
• Non-code change (docs, etc)
• None of the above: (explain here)

Test Plan

Unclear, the current strategy for testing query doesn't actually generate a response.

[jhamon]

I see what you're saying. I'll try to add some tests for this codepath.

[jhamon]

I had to make a lot of other changes in this neighborhood of the code to fix some problems with timeout handling. So this was addressed as part of #510.