unbind last_operation response always responds with 410 Gone

[mhrivnak]

What happened:

When an async unbind operation is in-progress, the last_operation endpoint incorrectly responds with a 410 Gone response code.

This is on the release-1.1 branch.

What you expected to happen:
The spec says a 410 response to a last_operation request is "Appropriate only for asynchronous delete operations. The Platform MUST consider this response a success and remove the resource from its database."

In our case, a 410 response does not indicate success because it gets returned even while the job is in-progress. Thus our response is misleading.

How to reproduce it:
Use the last_operation endpoint to query the state of an in-progress unbind operation.

Cause
This is likely caused by the fact that when the DELETE is requested on the binding, the BindInstance is deleted from etcd before even a 202 response is returned. It may be better to do that deleting at the end of the unbind job.

[philipgough]

/assign I'll take a stab at this one.